Osamu Dazai/Relationships

Armed Detective Agency=

|Naomi-chan


 * -|Port Mafia=

|Akutagawa-kun


 * -|The Guild=


 * -|Rats in the House of the Dead=


 * -|Special Division for Unusual Powers=


 * -|Others=

Doppo Kunikida
"He's someone who can stand at the forefront… One who's strong, unwavering, and aware of his weaknesses. A person capable of rising above everyone else. The next in line… could only be Kunikida-kun."

- Dazai recognizes Kunikida's leadership qualities

Kunikida is Dazai's partner in the Agency, with whom he shares opposite traits. Ever since their first meeting, Dazai frequently likes to tease and make Kunikida angry to the point of ruining his ideal schedule for a day, even to the point of desperately finding ways to disrupt his schedule. He also tends to tell Kunikida various trivia and seemingly vital information for Kunikida to jot down in his notebook, only for Dazai to usually retort that they were merely jokes, which naturally irritates his partner.

During the initial phase of their partnership in the wake of the Azure Apostle's messages, Dazai and Kunikida were able to track down the mastermind behind the messages in spite of various peculiarities along the way, including Dazai's shady past, rare nullification ability, and enigmatic character. This eventually reached a point when Dazai admitted that he is the Azure Apostle, only for Kunikida to see through this façade and successfully deceive the real Azure Apostle. At this point, Dazai asserted his trust towards Kunikida, knowing that the latter would not aim a gun at other people out of the blue without hearing a needed explanation.

Despite their boisterous partnership, Dazai and Kunikida grew to share a mutual trust towards each other, quite apparent during cases in the field. Even during their first time as partners in the Agency, Dazai's instincts especially during combat complimented Kunikida's, such as when they respectively fought a big man and a blond man. After figuring out that they had to switch foes, it merely took calling out to each other to signal and acknowledge their similar plan, resulting to their victory. In the anime, Atsushi witnesses Dazai and Kunikida collaborate together and praises their complementary dynamic.

As a result, Dazai and Kunikida turned into the most talented duo in solving tough cases in the Agency, holding a record of having solved the most difficult cases since Dazai's entrance to the Agency. Notably, people who do not know their contrasting personalities usually thought they make a perfect pair. After all, Dazai's carefree attitude and Kunikida's rigid strictness appear to be one of the causes of their usual banters. However, though Dazai is one of the greatest sources of Kunikida's annoyance, the latter views Dazai as one of their prized detectives, accomplishing case-related tasks at Dazai's behest sometimes without being told for what reason.

On a deeper level, Dazai is quite aware of Kunikida's idealism, criticizing that people like Kunikida and the Azure King who believe in the existence of an ideal world end up resenting the world and hurting others when unable to attain their goals. He ultimately warns Kunikida that getting too entrenched in pursuing his world of ideals shall soon result to him harboring the Azure King's rage and, consequently, losing everything and everyone around him.

Nevertheless, Dazai acknowledges Kunikida as one who can instill beliefs in other people, can skillfully handle affairs, has an unwavering character, and is aware of his own limits and weaknesses. With these qualities, Dazai recognizes Kunikida as a role model and the next ideal President for the Agency.

Atsushi Nakajima
"Stop feeling sorry for yourself. As long as you do… your life will be an unending nightmare."

- Dazai advises Atsushi

On their first meeting, Dazai was saved by Atsushi from drowning, though Dazai retorted that he was actually committing suicide. Through this chance encounter, Dazai came to know Atsushi's recent expulsion from his orphanage and eventually deduce that their erstwhile target, a man-eating tiger, is Atsushi himself. After taking a glimpse at Atsushi's low self-esteem, Dazai decided to hire him into the Agency. In truth, Dazai had wished to test a theory whether Atsushi can take on the mantle of being half of a new Twin Dark with Akutagawa, in order to prepare for the "real catastrophe" lurking within Yokohama.

Along the course of events, Dazai serves as a mentor figure towards Atsushi. Despite Atsushi being frequently caught up in Dazai's eccentric shenanigans, Dazai would nonetheless offer some pieces of advice towards the rookie detective regarding various fields. Furthermore, Dazai's theatrics do not take away his serious persona towards Atsushi and more often than not shows genuine care and attention towards the youngster. In some instances, Dazai would snap Atsushi out of wallowing in self-pity, even to the point of slapping him and asking him not to pity himself. Essentially, Dazai appears to perceive Atsushi as a capable individual with a lot of potential, which is one of the reasons why he chose to recommend Atsushi to the Agency.

Outside their professions, Dazai remains a mentor figure towards Atsushi and gives him some advice during pressing instances. In one occasion, Dazai acknowledged how the orphanage director from Atsushi's childhood left an undeniably negative mark in his life, though he later ambiguously remarked how his past experiences might have also shaped the way he grew up and stood back up many times. In the end, Dazai left Atsushi to reflect and gather his inner turmoil, letting him make his own expressions as his feelings decide. This soon became a turning point in Atsushi's life, during which his visions of the orphanage director gradually get replaced with Dazai's apparitions, signaling a seemingly establishment of their mentor-mentee relationship.

Throughout most of their endeavors, Dazai would pair Atsushi with Akutagawa, thinking that they could be a new incarnation of Yokohama's Twin Dark, albeit unbeknownst to both Atsushi and Akutagawa. Although Atsushi voices out how incompatible their combat styles and general methods are, Dazai would continually have them work together and subtly attempt to have them complement each other's abilities rather than fight individually. Furthermore, behind Atsushi's back, Dazai even sought out Akutagawa's cooperation in order to save the Agency, the world, and Atsushi's life along the process—a request that Akutagawa reluctantly accepts.

Yukichi Fukuzawa
Dazai and Fukuzawa have a positive professional relationship. Dazai respects Fukuzawa as their President and, likewise, Fukuzawa treats Dazai like any of his subordinates. Prior Atsushi's entrance exam, Dazai sought the President's approval regarding hiring the mantiger, to which Fukuzawa assigned him to oversee the entrance exam. After Atsushi passes his exam, Dazai asked for Fukuzawa's decision once more, with which the President approved Atsushi to be under Dazai's care, showcasing their mutual trust. In the anime, Dazai initially recommended Atsushi to Fukuzawa. Since the President believes that power does not make one a member in the Agency, Dazai used this very premise to suggest hiring the youngster into the Agency.

Like other members of the Agency, Dazai holds utmost regard towards the President. Given his laid-back attitude, Dazai would choose to carry out the President's tasks even during times of utter boredom. In a similar way, the President would personally participate in Dazai's schemes in the most vital scenarios. One such case is Kyōka's entrance exam, which was planned by Dazai and Ranpo to have the President activate his ability with and save their newest official member during the process.

Ranpo Edogawa
"That was incredible! You are without a doubt an extraordinary detective! I'm so glad I joined this agency!"

- Dazai praises Ranpo's deduction skills

Hailed as the Agency's sharpest detectives (双璧,), Dazai and Ranpo are the organization's intellectual group. Dazai first met Ranpo as a newcomer in the Agency, during which he witnessed Ranpo's Super Deduction firsthand, only to find out that Ranpo is a non-ability user after touching his hair while deducing and failing to nullify it. This earned Dazai's great respect towards Ranpo's genius intellectual prowess and pure deduction ability, which also shocked Kunikida after finding out about it for the first time through Dazai. As a result, Dazai and the rest of the Agency members respect Ranpo despite the way he behaves in the Agency.

Later on, Dazai's and Ranpo's collaboration are explicitly shown while planning the Moby Dick infiltration. Their conversation, through Atsushi's perspective, merely consisted of audibly vague ideas, though the both of them seem to have a mutual thought process and understanding as to how they shall go about their scheme, which ultimately led to their success.

This unseen dynamic apparently persists in various instances, such as after the Yokohama fog incident, specifically when Ranpo returns back to reality and ambiguously calls out to Dazai while musing on the events he predictably deduced. In one of their cases in Standard Island, Dazai made sure to contact and update Ranpo after sensing in advance that the agents would be in trouble, hence leaving the rest of the matter in Ranpo's hands and eventually saved the Agency members and many people in the island.

Kyōka Izumi
"See… Kyōka-chan, you don't know everything about our Agency or yourself. Nobody can truly know it all. That's where one's 'potential' comes in."

- Dazai to Kyōka

Dazai first met Kyōka when she was still part of the Mafia on orders to bring him to their base. Eventually, when Kyōka becomes an unofficial part of their team, Dazai advises Atsushi to take care of Kyōka as her roommate, which Atsushi enthusiastically accepts.

Later, during Kyōka's arrest in the course of the three-way conflict, Dazai communicates with her in an attempt to change her outlook and perspective in life. Though Kyōka was hopeless regarding her situation as a former assassin, Dazai gave her another chance and assured her that she is not entirely unfit to be part of the Agency. In the end, his words channeled a sense of renewal in Kyōka, who was then willing to sacrifice her life to save Yokohama, paving way to her official entrance to the Agency after passing her secret entrance exam.

Akiko Yosano
Like the rest of the Agency members, Dazai views Yosano as a vital asset to ensure their survival, hence having his fellow members to protect her at all costs during the three-way organizational conflict with the Mafia and the Guild. On another note, Dazai seems to agree with Yosano's belief that "death is the fairest judge of all".

Jun'ichirō Tanizaki
Dazai and Tanizaki have a harmonious work relationship, with Dazai treating Tanizaki like any other subordinate. As such, Tanizaki is subject to witness Dazai's theatrics despite being more senior than Tanizaki, who once thought how evil Dazai's plot was when he invited Master Carlyle to the Agency office just to disrupt Kunikida's schedule.

Nonetheless, Dazai occasionally contacts Tanizaki during work-related instances, such as during Dazai's absences or as backup. Moreover, Dazai once asked permission from Tanizaki to have his sister act as a hostage for Atsushi's entrance exam when he "thought" he was going to act as the bomber.

Naomi Tanizaki
Dazai once presumably advised Naomi that, in case one shares the same intel with the enemy, the side who does the unexpected wins, but one loses by default when the enemy gains more intel. This later helped Naomi and Kirako Haruno a chance to prematurely escape from John Steinbeck and Howard Phillips Lovecraft during the Guild war.

Kenji Miyazawa
As with other Agency members, Dazai has a good rapport with Kenji. Because of the latter's innocent and direct ideas, even Dazai appears to sometimes be speechless with his suggestions when asked.

Chūya Nakahara
"They started to call us 'Twin Dark'… the day we used Corruption to level a building and the enemy force inside. But… if my support lags behind at all… you'll be dead, Chūya. So you make the choice."

- The dynamic between Dazai and Chūya's Corruption

Dazai and Chūya were former partners when Dazai was still part of the Port Mafia, forming the team Twin Dark (双黒,). They were well known as Yokohama's vicious duo and 'the criminal world's worst enemy' both inside and out of the Mafia, though they both expressed distaste for being forced to work together under Mori's orders.

Their first encounter was on Dazai's search mission for the previous Mafia boss's apparent resurrection at Suribachi City. Chūya kicks Dazai to the ground and demands to know the Mafia's intel on Arahabaki, who is rumored to be connected to the return of the previous boss. Dazai refuses, instead tells Chūya to kill him instead, and recognizes him as the infamous King of the Sheep, calling him a 'cocky, over-confident child', while Chūya retorts with calling the 'suicidal brat' Dazai a 'condescending little prick'. In their ensuing fight, the previous boss appears and decimates the area, and Dazai manages to capture Chūya at the cost of a broken arm.

Chūya is then taken to the Mafia headquarters, where Mori offers him to affiliate with the Mafia by investigating the previous boss' reappearance, holding the Sheep members hostage. Mori then orders Dazai to find the person responsible for the events, making Chūya his partner, much to the pair's displeasure and irritation that began their partnership.

Throughout this, Dazai is shown to resent Chūya's excessive use of violence and over-the-top methods of defeating the enemy, while Chūya scorns Dazai's suicidal tendencies and more strategic approaches. Chūya is also slightly irritated by the fact that Dazai took Chūya's title of the Port Mafia's youngest executive away from him.

After the events of the Dragon's Head Conflict, the pair were called Twin Dark after they had defeated an enemy organization in a short amount of time that night. Their partnership dissolves when Dazai suddenly leaves the Mafia, specifically after Sakunosuke Oda's death.

Even though the pair often express their mutual hatred and contempt for each other, they have absolute trust in one another, Chūya using Corruption on multiple occasions and placing his life on the line believing in Dazai's abilities. Having known each other for so long, they can even predict the other's thinking, logic, and moves, Dazai even stating that he can predict all of Chūya's attacks, kicks, and punches.

Sakunosuke Oda
"He was a friend of mine. He's the reason I quit the Port Mafia and joined the Agency. I'd probably still be killing people for the Mafia if it wasn't for him."

- Dazai tells Atsushi about Oda anonymously

While Dazai was an executive of the Port Mafia, the lowest-ranking member Oda was his best friend and, as Dazai stated, the only one who could come close to understanding him. Along with Ango Sakaguchi, he and Oda were drinking buddies. Other members of the Port Mafia often remarked that it was odd that the lowest-ranking member was friends with an executive. However, behind Oda's back, Dazai warned them about the mafioso's strength and skills that surpass even Akutagawa's, indicating his firm belief in Oda's capabilities as a gifted marksman and in general.

As the friendship among the three mafioso started to collapse, Dazai confessed to Oda and Ango that he knew very well about the intrinsic probability of losing the ones he does not wish to lose the most, hence anticipating such thing to happen anytime in his life. Dazai later opened up to Oda that he joined the Mafia in his quest to find a reason to live. He thought that being close to death and violence would make him witness the rawness and inner nature of humankind firsthand. However, though Dazai asked Oda to expect good things to come and redirect his focus on other aspects of life, Dazai was unable to dissuade Oda from heading into his battle alone. Eventually, Dazai requested Mori to send reinforcements for Oda for the mere reason that he was his friend amidst Mori's reproach.

Nonetheless, Dazai managed to catch up to Oda's location, albeit arriving at the sight of him and André Gide having shot each other. As Oda laid dying, he advised Dazai to turn to the side that saves people and become a good man who saves the weak and protects orphans, knowing that good and evil mean little to him. In this way, Oda believed that it would make Dazai a bit better, a final thought he imparted to Dazai as his friend. As a result, Oda became the reason Dazai left the Port Mafia.

Across various times, Dazai would continually recall Oda in his thoughts and contemplations. He would frequent Bar Lupin and reminisce past conversations with Oda by himself, as well as occasionally visit Oda's grave. It is also hinted in many instances that Dazai's advices and thought processes stem from or are influenced by his interactions with and remembrance of Oda, including how a former assassin can change into becoming good people, recalling a mafioso who does not kill, and how the ones who truly make the world turn are those who act according to uncertainty.

Ryunosuke Akutagawa
"The enemy won't wait for you to stand back up. On your feet! Use your ability to counterattack! You cannot survive in the Mafia on something so paltry! Or… do you want to go back to life in the inner slums?"

- Dazai training Akutagawa

When he was promoted to the rank of executive, Dazai first met Akutagawa in a certain forest and gave him an option to be recruited under Dazai's direct commanding unit. Dazai once admitted being horrified when he first saw the boy in the slums for his extraordinary yet destructive ability. Seeing how stubborn Akutagawa was, Dazai thought that the boy would have ended up being a slave to his own powers until he destroyed himself.

Though Akutagawa was initially reluctant of Dazai's offer and even attacked him with his ability, Dazai promised to give him anything he wished for, despite not guaranteeing that it would be an easy path to undertake. Akutagawa nonetheless responded that he wanted a reason to live, which Dazai assured to grant and wrapped his black coat around Akutagawa, formally welcoming him into the Mafia.

Under his direct unit, Dazai trained Akutagawa rigidly to hone his ability, combat skills, and fortitude, usually resorting to harsh and forceful bouts to have Akutagawa refine Rashōmon. Using his nullification ability and physical prowess, Dazai personally fought Akutagawa and lectured him to aggressive lengths, warning him to fight back whenever needed to last long in the Mafia, lest he would return to being a stray dog. In essence, Dazai viewed Akutagawa as a sword without a sheath; though he believed Akutagawa has the potential to be the Mafia's strongest ability user, Dazai thought then that someone needed to teach him how to put that sword away.

Dazai would also lecture (not far from punish) Akutagawa for his misdeeds, such as the time when Akutagawa killed off their remaining leads on Mimic that earned Dazai's anger. After punching Akutagawa's face, Dazai shot at him three times, which unwittingly let Akutagawa unlock Devoured Space. Dazai rebuked his all-offensive thinking and casually told him how he can also use his ability for defense. He chided his subordinates' perception that the Mafia is all about killing others and compared Akutagawa to Oda, whom he believed to be way superior than Akutagawa himself.

Upon leaving the Mafia, whenever they would cross paths, Dazai retains a rather aloof and cold demeanor towards Akutagawa. During the Agency's and Mafia's earlier conflict, Dazai maintains his dry humor but communicates with Akutagawa with subtle contempt, even telling his former protégée that his new subordinate is far better than him. Later on, however, Dazai is not entirely oblivious to Akutagawa's development, occasionally partnering him with Atsushi to have them collaborate in hopes of turning them into a new Twin Dark. At one point, Dazai complimented Akutagawa and acknowledged his development, and he also trusted Akutagawa to be his eyes during the Decay of Angels' terrorism plot.

Ōgai Mori
""You were afraid, weren't you, Mori-san? Afraid I'd cut out your windpipe and assume the boss' seat. Just as you did to the last boss."

- Dazai exposes Mori in front of his subordinates

For reasons still vague, Dazai and Mori met by fateful encounter; Dazai, who attempted suicide when he was 14 years old, was presumably attended to by Mori as a physician. During this time, Dazai and Mori became "collaborators" in carrying out the then Port Mafia boss' assassination. As a result, Dazai became the only witness of Mori killing the boss and claiming the position of Mafia boss. Dazai, however, claimed that Mori miscalculated making an accomplice out of him. Contrary to his strategy that Dazai would die shortly after the incident due to his suicide, Dazai has not died then, further planting anxiety in Mori as long as Dazai is alive and knows about the previous boss's assassination.

A year later, Dazai and Mori formed an ambiguous relationship, in which Dazai was not considered a subordinate of Mori nor of the Mafia. Even when Mori became the head of the Mafia, Dazai's nightmarish and intimidating thoughts challenged Mori's strategizing, so much that he could not move easily or recklessly in Dazai's presence with his unstable reputation as the new Mafia boss at the time. Nonetheless, Dazai accepted Mori's assignment to investigate the alleged reappearance of his Mafia predecessor in exchange for medicine that can grant him a "comfortable death".

Dazai admitted how he found annoying authorities with troubling ideas to be his entertainment, later making Mori remind the young Dazai of himself. Along the process under Mori's orders, Dazai displayed no signs of affiliation towards Mori, even lying that he saw the deceased predecessor in Suribachi City (only to indeed witness the predecessor "appear" later on). His seemingly instrinsic boredom, however, might have outweighed his choice to reject Mori, which is possibly the reason he blankly carried out Mori's instructions and acted under his orders, including partnering with Chūya with whom he is in great disagreement.

Eventually, Dazai accepted the offer to join the Mafia, much to Mori's pleasure. He was immediately given command over a unit and a job, which was to dispose their erstwhile adversaries. In his time as Mafia executive, the young Dazai was taught various war strategies by Mori himself, including tactics studied by Schelling, Nash, and Kissinger. Moreover, despite his natural genius and intimidating aura, Dazai erstwhile felt to be walking on blades whenever he talked with Mori, aware how one minute mistake could possibly throw him off the path.

Though their relationship was far from harmonious, Dazai's rapport with Mori began to sour during Mimic's illegal entrance to Yokohama that eventually jeopardized the Mafia and his friend Sakunosuke Oda's life. To his dismay, Dazai figured out that Mori led Mimic into Japan all for the sake of acquiring a skilled business permit from the Special Division for Unusual Powers. Much to his apprehension, Dazai knew Mori's calculations and rationale behind his scheme for the welfare of the Port Mafia, logically how Mori was right and Dazai wrong amidst his reasons of how Mori led Oda into fighting Mimic by himself. Dazai then chose to disobey Mori's orders, knowing that Mori would not have him executed and simply stating that Oda was his friend.

In the end, upon Oda's death, Dazai chose to defect from the Mafia. Mori, in return, left his executive spot open and claimed how the Mafia would get boring without Dazai. Around or after this time, Dazai apparently burned the coat that Mori bought for him.

Years later, Dazai would carry the knowledge of Mori secretly assassinating his predecessor and utilize it at times as a casual yet dark source of banter with Mori, also possibly to display his disdain for the Mafia boss. Moreover, Dazai firmly denounces having the Agency collaborate with the Mafia, specifically after the Guild's attempt at incinerating Yokohama. Nevertheless, amidst the circumstances, Dazai ends up acting according to the two parties' interests with working together for the sake of defeating their mutual adversary. At such times, Dazai exudes an aloof and cold demeanor towards Mori despite the latter's usual enthusiasm towards Dazai, thought not to the point of blankly rejecting or ignoring Mori.

Kōyō Ozaki
Before becoming an executive himself, Dazai seemed to have held respect towards Kōyō when he exclaimed how someone like Chūya got to be assigned under her direct supervision, though this might as well be Dazai insulting Chūya at the time. Nevertheless, during Dazai's time as Mafia executive, their units appeared to have worked together at times in interrogating their captives, with no one said to have not spilled everything during Dazai's intervention. After Dazai defected from the Mafia, Kōyō perceived Dazai as a traitor in the organization, a feat he viewed lightly.

However, as adults, Dazai and Kōyō are able to meet halfway and compromise, agreeing at one point regarding Kyōka's welfare. Given Dazai's knowledge on how Kōyō once attempted and failed to escape into "the light" with her lover away from the Mafia, he uses this to contradict how he sees Kyōka's potential to change. This prompted Dazai to plan impeccably and eventually have Kyōka pass her secret entrance exam after she chooses to sacrifice her life and save others—a trait Kōyō believed is practically improbable with yet longed to happen to Kyōka. Moreover, Dazai knows how Kōyō deeply cherishes and wishes to bring Kyōka into the radiant world, so he promises not to let her past befall Kyōka and even urges Kōyō to show Kyōka the light herself.

Ryūrō Hirotsu
"The reason you have so many people following you is that you don't turn your back on them. I'll leave things in your hands. I won't tell the boss."

- Dazai covers for Hirotsu

In investigating about the previous Mafia boss's alleged reappearance, Dazai once nominated Hirotsu to be his escort around Suribachi City, since he knew the upper land around the area. Dazai appeared respectful towards the Mafia veteran and even warned him not to fight Chūya during their encounter after figuring out his gravity manipulation ability. On the other hand, Hirotsu's initial instinct doubted and distrusted Dazai, a Mafia outsider, but he nonetheless abided by and escorted the youth with his typical professionalism, most likely as he is under jurisdiction given by Dazai's Silver Oracle.

When Dazai became an official Mafia member and rose to the ranks of executive, he maintained a rapport with Hirotsu, albeit also retaining his satirical and enigmatic attitude. Dazai also saw through Hirotsu's way of leading his subordinates, warning him to dispose of his unworthy and sloppy subordinates before they can endanger his reputation and possibly the organization. However, this turned out to be another one of Dazai's theatrical showcases and instead recognized how Hirotsu does not turn his back on his subordinates, which in turn earns him their loyalty; the young executive even covers for Hirotsu by promising not to tell the boss about Hirotsu's own cover-up of his subordinate's failure.

After Dazai left the Mafia and joined the Agency, Hirotsu appears to be one of the mafiosi with whom Dazai chooses to be in casual contact, seemingly retaining a formal relationship with each other despite all that happened between Dazai and the Mafia. The two even occasionally shares some laughs by telling stories from the past. Quite unlike his carefree or dark character, Dazai expresses his gratitude towards Hirotsu's help during the Guild war and even shares with him how he wished to test Atsushi's and Akutagawa's compatibility and potential to be a new generation of Twin Dark.

Kyūsaku Yumeno
"I still remember it well. Sealing away you and you alone… cost many lives. But there will be no sealing next time. I'm going to pluck your heart out."

- Dazai grimly reunites with Q

Dazai first met Q when the latter was brought in by Mori from a hospital into the Mafia headquarters. Not knowing what Q's ability was or how it worked, Mori then assigned Dazai to look after the child, with his nullification ability in charge of neutralizing Q in case of emergency. Though Q cheerily introduced themself to Dazai and asked him to play with them, Dazai merely responded indifferently to do so when they get bigger.

At one point when he was in the Mafia, Dazai played a crucial role in sealing up Q after an incident that claimed various lives due to their ability. Seemingly since then, Dazai perceived Q as a deprave ability user who does not differentiate between friend and foe and a walking disaster bent on destroying everything along their path. As a result, Q detested Dazai and vice versa, with Dazai darkly promising to "pluck out Q's heart" the next time they meet.

Gin Akutagawa
"We all change over time. I mean, look at Gin-chan over there. She used to be a sweet little girl, no taller than this!"

- Dazai describes Gin in the past to Higuchi

Dazai fondly calls Gin and treats her casually, even when she holds him at knife-point. He also casually remarks on Gin's appearance over the years as a "little girl" in the past, earning the Black Lizard commander's shyness in his and Higuchi's midst.

Arthur Rimbaud
"A European Intelligence agent? A 'Transcendent' class of only a few dozen gifted with the highest rank in the world? Randō-san, you can't be serious."

- Dazai learns about Randō's real identity

Before joining the Mafia, Dazai had known the Mafia sub-executive Randō and his hyperspace ability, as well as his sole survival in the most recent Arahabaki explosion at the time. Dazai also did not seem to mind Randō's unusual remarks about being cold, even at times throwing in logs to his fireplace to help heat the room. After all this amicable façade, when Dazai uncovers Randō as the perpetrator behind the previous boss's reappearance, they initially appeared to maintain an unhostile rapport; Dazai "helped" further their conversation, as Randō claimed he did not know how to act nor speak as a criminal.

Later on, while battling Rimbaud together with Chūya, found Rimbaud's power to be quite unbelievable and became greatly shocked at its Transcendent-level extent. Moreover, Dazai would realize how Rimbaud did everything—including betraying the Mafia, resurrecting the previous boss with his ability, and fighting to kill Chūya—for the sake of his past friend, though he admittedly found it hard to believe.

Ichiyō Higuchi
"You are stunning. Such fleeting glory, like the petals of a water lily… and such touching sweetness! How would you like to join me in a lovers' suicide—?"

- Dazai to an undercover Higuchi

It is unclear whether Dazai had known Higuchi before her undercover request at the Agency, but Dazai highly complimented Higuchi's beauty upon their seemingly first encounter. This turned out to be partially a feint, as Dazai used his theatrics to plant a listening device in her pocket after sensing an ulterior motive from her.

Later on, Dazai turns indifferent towards her threats to the Agency on what the Mafia can do to them, since he himself was once part of the Mafia as Akutagawa revealed. Moreover, Dazai would not fold towards Higuchi's later threats, such as holding him at gunpoint, and retorts that she would hardly be an optimal choice for his assassination, claiming that a huge number of volunteers would be involved if the Mafia were to carry out such task.

Ango Sakaguchi
"Good to see you here, Ango. What on earth made you think… that I had forgiven you?"

- Dazai's grudge towards Ango

During his days as a Mafia executive, Dazai and Ango, along with Oda, were drinking buddies and would talk about their work without their positions nor ages get in the way of their mundane conversations. They frequently ran into one another for some reason, a gathering which Oda thought is a guise of communication in trying to avoid something. Oda also noted that the three of them would spend time in the bar until the dead of night.

However, their friendship started to collapse when Ango was uncovered to be a triple spy in the Mafia and the Special Division. Dazai confessed to Ango and Oda that he knew very well about the intrinsic probability of losing the ones he does not wish to lose the most, hence anticipating such thing to happen anytime in his life. Nonetheless, compared to Oda, Dazai seemed to have been affected by Ango's "betrayal" the most, especially since this eventually set off a string of events that led to Oda's death, despite the entire scheme being manipulated by Mori since the beginning.

Years later, as a result of their fallout, Dazai appears to hold a grudge towards Ango. When he contacted the latter during the three-way conflict, Dazai verbally asserted how he seemingly has not yet forgiven Ango most likely due to the Mimic incident. Ango merely responded how he was the one responsible for cleaning Dazai's ledger, to which Dazai retracted holding him at gunpoint and eventually sought out the Special Division's help in the Guild war, only for the both of them to be embroiled in a car accident. In the end, Dazai ambiguously answered with a dark smirk when Ango inquired how he was the only one seriously injured from the accident, indicating a probable hint of his involvement in the incident.

During the Decay of Angels' terrorism plot, Dazai notably chose Ango to be his middle-man while imprisoned in Meursault. Given his past with and apparent bitterness towards Ango, Dazai's ulterior motive of choosing the latter—if any at all—is unknown, though this may be his optimal decision considering how Ango is a prime candidate as someone with ties to the government and can help him.

Santōka Taneda
Dazai sought the help of Taneda to find a new job after he left the Port Mafia. He was then asked if he was willing to join the Special Division for which he refuses, since he dislikes places with a lot of rules. Dazai was then referred and personally recommended by Taneda to the president of the Agency.

When Kunikida first asked him how he ended up joining the Agency, Dazai expounded how he happened to chance upon an "old guy"—Taneda—who was sitting next to him. Interestingly, Dazai narrated how Taneda promised to give him a job if he beats him at a drinking contest, with which Dazai jokingly went along. In the end, Dazai won their bet, which then followed how Taneda was implied to have recommended him to the Agency.