Atsushi Nakajima/Relationships

Orphanage Director
Atsushi carries hatred and deep fear toward the Headmaster of his orphanage, who acted as his caretaker. His negative feelings are due to the Headmaster torturing and abusing him verbally, physically, and emotionally throughout his entire life, up until he was thrown out of the orphanage.

Upon the Headmaster's death, Atsushi goes through emotional turmoil and confusion. Dazai helps him realize that he became someone who understands suffering, resists violence, and saves people. However, Dazai also tells him the treatment he went through was barbaric, and that Atsushi obviously is under no obligation to forgive him. When confused about how he should feel, Dazai tells him that usually one cries when losing a father. To this, Atsushi cries in both bereavement and relief.

The abuse that Atsushi suffered under the Orphanage Director's hands still affects him in his day to day life, which was severe enough to give Atsushi daily nightmares and flashbacks, and cause him to hear regular phantoms of his voice as the source of his internal self doubt. He carries so much fear that seeing a mere image of his Headmaster is enough to cause him to panic, and he remarks that the fear he felt in that moment was more intense than even his most tense battles.

Osamu Dazai
Dazai is the first member of the agency Atsushi meets, encountering him when rescuing him from drowning in a river. Dazai quickly assumes responsibility for him, taking him to eat and happily conversing with him. He bribes Atsushi to become bait for the tiger since Atsushi admits that it had been "following" him. Upon discovering that Atsushi himself is the tiger and an ability user, Dazai recommends him to the agency and even walks with him to his entrance exam, under the guise of taking him to a job interview.

Once in the agency, Dazai takes over as his supervisor. Throughout the events, he mentors and advises him, sometimes in the form of teasing or playfully taking advantage of him, such as asking Atsushi to write a report for him. Atsushi remains trusting, albeit bemused at Dazai's constant fluctuations in demeanor and priorities.

They form a closer relationship between them; Dazai often talks Atsushi through his several breakdowns, showing concern for his wellbeing in his eccentric way. In one notable and slightly more harsh instance, when Atsushi panics after harming Naomi and Haruno under Q's ability, Dazai slaps him and sternly tells him that pitying himself will make life an endless nightmare, ultimately snapping him out of a panic attack.

Doppo Kunikida
Kunikida is skeptical of Atsushi upon his arrival, shown when he scolds Dazai for spending his money on him and his proposition for Atsushi to join the Agency. Their ideals also clash a couple of times when Kunikida discourages him from trying to save Kyōka, telling him that he can't save everyone (most likely based on past experiences rather than strict ideals.)

As events progress, Kunikida and Atsushi have more of a mentor/mentee relationship, the former shown training him in the martial arts he learned from Fukuzawa and giving him advice.

Ranpo Edogawa
Being a new Agency member, Atsushi often wonders about Ranpo's words and actions. He is surprised to witness Ranpo's lack of what seems to be common knowledge, such as how to ride a train- he doesn't know how to buy a ticket or which platform to go into.

Atsushi's respect grows for Ranpo as he learns more about him, though he remains confused about the man. However, they are on friendly terms, Atsushi going so far as to letting Ranpo climb on his back for a ride.

Yukichi Fukuzawa
Like most other members, Atsushi has a healthy amount of respect towards Fukuzawa. He is slightly intimated by the severe man but still obeys him.

Akiko Yosano
Atsushi respects Yosano a lot, despite being afraid of her treatment. He doesn't seem to mind carrying her bags and boxes. He admires her for her strong will and attitude.

Kenji Miyazawa
Atsushi is partnered with Kenji when they investigated a car explosion incident. Though Atsushi thinks that Kenji's methods of investigating were questionable, he later then dismisses it and follows his lead. Due to naivety and how simplistic Atsushi is, he ends up finding Kenji's methods to be standard, until the pair get surrounded by a group of dangerous criminals, and Atsushi realizes that Kenji's methods work best for him alone due to his personality and ability. As Kunikida states, they are the best and worst team together.

Kyōka Izumi
Atsushi first encounters Kyoka when he assisted Yosano in shopping. He later founds out Kyoka has killed 35 people and wants to stop killing others, he then saves her from the bomb explosion. As someone who understands what she has gone through, Atsushi deeply cares about Kyoka as to accompanying her when they explored Yokohama. He also tries to protect when someone tries to hurt her.

Jun'ichirō Tanizaki
Atsushi first meets Tanizaki during his entrance exam to join the Armed Detective Agency. After Atsushi has been accepted into the Agency, Tanizaki apologizes for being mean to him. For Atsushi's first job, he is paired with Tanizaki and Naomi to investigate supposed smugglers in the area.

In later events, Atsushi is paired with Tanizaki once again by Ranpo to investigate the death of his orphanage director. Upset from seeing his orphanage directors face, Junichiro brings Atsushi coffee and attempts to console him, thinking Atsushi is sad from the death.

Though Atsushi and Tanizaki are of the same age, Atsushi calls him Tanizaki-san. This could possibly be due to Atsushi's feelings of inadequacy.