Yukichi Fukuzawa/Synopsis

Armed Detective Agency vs. Port Mafia Arc
Fukuzawa's first appearance takes place after Atsushi took his "entrance exam" at the Agency. Because of the young man's ability to transform in a feral, giant tiger, the President wanted to test Atsushi's spirit. Fukuzawa eventually hires Atsushi and places him under Osamu Dazai's care.

After Atsushi's abduction by the Port Mafia and with several Agency members agreeing to leave the young man to his fate, Fukuzawa steps in at Naomi Tanizaki's initiative. Despite his organization entrusted at that time with the task to protect some government officials, Fukuzawa orders all Agency members to drop the mission until Atsushi's safe return, as, according to his words, nothing can be more important than saving a companion in danger. He is later seen along with his subordinates, talking about potential leads in Atsushi's disappearance. After hitting a dead end, he asks for Ranpo and his deductive-reasoning skills in exchange for the President praising him. With Ranpo having found where Atsushi is, Fukuzawa gives Kunikida the key to the Agency's boat and asks him to bring Atsushi back at all costs.

With Kyōka and Atsushi out of danger, Fukuzawa summons Kyōka's presence at the Agency. The young girl requests her right to stay from Fukuzawa who, having a very soft spot for cute things including Kyōka's face, cannot refuse. When police officer Minoura suspects Kyōka to be the young girl who is on the police wanted list for being a murderer, Fukuzawa eventually claims Kyōka to be his granddaughter. Minoura believes him as both wear the same stern looks and is "cut from the same mold".

The Guild Arc
When members of an American organization called The Guild pay a visit to the Agency, the leader of the Guild, Francis Fitzgerald, offers Fukuzawa a great amount of money in exchange for the Ability Business Permit, a document granted by the government allowing the Agency to run ability-based business. Fukuzawa dryly refuses, telling Fitzgerald that neither the lives nor the permit of the Agency can be bought, as the permit embodies the hope of the government and Natsume's efforts to found the Agency.

Riled up because of the bloody encounter between several members of the Guild, the Agency and the Port Mafia, with the former being victorious, Fukuzawa goes for a walk, unaware of Ōgai Mori's assassination plot against him. While discussing the upcoming evacuation of the Agency with Kunikida by phone, the President is attacked by second-class assassins. It soon appears that Fukuzawa is more than able to deal with them, thus revealing his unchallenged efficiency in martial arts. He gives the beaten assassins a threatening message for whoever is behind the murder attempt, warning them against laying a single finger on his subordinates; instead, he urges them to come at him and him alone.

Soon after, he is seen entering the new Agency hideout, warning his subordinates against the Guild and the Port Mafia since both organizations are seeking the demise of the Agency in the near future. Fukuzawa finds himself assigned to the defense team as protecting Akiko Yosano is the key to the survival of the Agency in the upcoming war. He is revolted when he learns that the Port Mafia used two of the Agency's clerks, Haruno and Naomi, as baits against the Guild.

After the large-scale Guild attack on Yokohama, Fukuzawa is seen giving treats to a cat during one of his walks; Atsushi appears, and the two engage in a long conversation. The President is asked by Atsushi to implement a temporary truce with the Port Mafia in order to overpower the Guild. As Dazai points the danger of such a meeting out to Fukuzawa, warning him about assassination attempts against the President, the latter replies that it is preferable to seeing his subordinates injured or dead.

At the meeting with Mori and the Port Mafia, Fukuzawa explains that while he is opposed to side with an illegal organization and therefore rules out an alliance, he advocates for a détente because of Atsushi’s plea. Mori points up the mutual grudges against each organization’s members and, above all, the lack of guarantees in Fukuzawa’s demand, as both the Agency and the Port Mafia could break the agreement without fearing sanctions. Fukuzawa offers to settle the score, “right here, right now”. With great speed, the two leaders attack each other, only to call it a draw as Fukuzawa puts his katana on Mori’s throat and Mori his scalpel on Fukuzawa’s. The President of the Agency eventually calls for a one-night truce in the name of their shared love for Yokohama and their status as protectors of the city against foreign ability users.

After the fall of the Moby Dick in Yokohama bay, Fukuzawa explains his ability to Atsushi who believes Kyōka to be dead because of the crash. All Men Are Equal only affects Fukuzawa's subordinates, inhibiting their powers so they can control them. Because she was willing to sacrifice herself in order to save Yokohama, Kyōka passed her own "entrance exam". She thus became a fully-fledged Agency member, fell under the range of Fukuzawa's ability and escaped moments before the crash thanks to her new control over Demon Snow. . He is later seen attending the welcoming party for Kyōka at the Agency.

Cannibalism Arc
During one of his evening walks, Fukuzawa notices a trail of blood leading to a dark back alley. Following the stains, he eventually gets attacked by the Masked Assassin who targets ability users. At first able to counter the attacks of the Assassin, the President gets shot by a sniper lying in ambush, barely grazing him but effectively poisoning him. Later revealed to be Nathaniel Hawthorne working for the Rats in the House of the Dead, the Assassin flies away, and Fukuzawa collapses on the ground.

He is later seen at the hospital under Akiko Yosano's care, but with the doctor's ability unable to cure him, Fukuzawa is still unconscious. With Ōgai Mori poisoned in the same way soon after, a strange sigil appears on Fukuzawa. At the same moment, Fyodor Dostoevsky explains to Dazai what is happening to the President: both him and Mori have been infected with Cannibalism, a lethal virus destroying the internal organs of the hosts after forty-eight hours. In order to nullify one host's affliction, the other has to die before the virus outbreak.

After examining the President, Yosano tells Tanizaki and Kunikida that Cannibalism is indeed draining Fukuzawa's life force. A distraught Ranpo holds a vigil at Fukuzawa's bedside. The situation quickly festers as both the Agency and the Port Mafia seek to kill the leader of the other organization to save theirs. All Agency members thus protect Fukuzawa's room against the enemy.

Thanks to Tanizaki's illusion ability and Kenji blasting through a wall, they are able to evacuate Fukuzawa from the hospital by ambulance. Tanizaki stays behind in order to frame the Port Mafia, Atsushi, and Kunikida chase the alleged virus ability user, and the President is taken to an unknown but hopefully safe location. Ranpo's stern but restless attitude shows Atsushi that Fukuzawa's situation is far more serious than previously thought.

When the President's eyes open again, he finds himself in Anne's Chamber, a dimension created by Lucy Maud Montgomery in order to protect him at Atsushi's request. As Lucy is taking care of a gravely ill Fukuzawa, he holds up a shaky hand and implores to not fight with the Port Mafia, and protect the balance and peace of Yokohama over his life.

The attempt to find the virus ability user failed, time is ticking, and Fukuzawa's orders to not attack the Port Mafia are discussed by the remaining members while the President is still looked after by Lucy. Fukuzawa awakes once more, notices a sleeping Lucy, and tries to sit up despite the pain. He is then horrified as he hears Atsushi announce Katai Tayama's death through a walkie-talkie given to Lucy by the Agency.

Fourteen hours before the virus outbreak, Fukuzawa finally manages to get up. Before he leaves Annie's Chamber, Lucy asks him to tell her what he plans to do, in exchange for her having taken care of him; to which he answers, "see an old friend". Soon after, Yosano is extremely concerned at the news that the President is gone. It is later implied during a conversation between Naomi and Kirako Haruno that Fukuzawa went on his own in order to protect the members of the Agency.

Without prior planning, Fukuzawa and Mori meet at an old mansion where they fought side by side for the first time twelve years ago. They agree that a duel to the death is the only way to end the bloody feud between the Agency and the Port Mafia. Mori summons Elise and promises Fukuzawa that this place will be his final resting place. Fukuzawa grasps his katana and readies himself to battle.

Twelve years ago, Natsume entrusted Fukuzawa with the task to protect Ōgai Mori who was still an active doctor at that time. Fukuzawa holds suspicions towards Mori as soon as he meets him. On the same night, he saves Mori from some local criminals looking for information about the Port Mafia, although the doctor was only pretending to be captured. Fukuzawa effortlessly takes out twenty guards on his own. He and Mori then talk about Natsume's Tripartite Tactic.

Back to the present, Fukuzawa and Mori are still fighting each other, thinking about how they were invincible when working together years ago. Fukuzawa eventually manages to cut Elise into pieces, calling for the end of the Tripartite Tactic. It is later revealed to be a plan made up by Natsume to preserve Yokohama's balance: the daytime for the military police and the abilities secret services, the nighttime for the Port Mafia, and the evening for the Armed Detective Agency.

Mori explains that his death would ignite an even bloodied war between the organizations, whereas Fukuzawa's death would bring the war to a peaceful end. He suddenly stabs Fukuzawa in the throat with his scalpel, then apologizes for his dirty play while his opponent is heavily bleeding on the floor. The apparition of Natsume Sōseki ultimately prevents Mori from dealing the final blow to the President of the Agency. Thanks to Natsume's intel, the Agency and the Port Mafia are able to track down the position of the Rats in the House of the Dead hideout and the virus ability user, Alexander Pushkin. When the man eventually exits the hideout, members from the Agency and the Port Mafia are waiting for him. Fukuzawa, alongside Mori, knocks Pushkin out, thus releasing him from the death sentence of the Cannibalism virus.

It is later implied that Fukuzawa made a complete recovery as a celebration is planned. While on a boat given by Fitzgerald, the Agency members apologize to Fukuzawa for having disobeyed his orders to not fight with the Port Mafia; the President says that the nature of their punishment will be decided later. He then congratulates them for their work on the matter and gives them a rare but genuine smile. Because they disobeyed Fukuzawa's orders, several members are given punishment such as helping a salesman at a shopping district (Ranpo) or being the target for target practice (Tanizaki).

Decay of Angels Arc
One month after the Cannibalism events, a formally dressed Fukuzawa is shown receiving a Shikyuu award (i.e. a bow made of cherry birch, named Azusa Yumi, usually used for Shinto rituals) during an official ceremony hosted by Vice-minister of Justice Tonan. The government thus acknowledges the major contributions of the Agency for public safety.

A terrorist organization named The Decay of Angels soon makes its presence known to the Armed Detective Agency by gruesomely murdering four government officials within a single week. Fukuzawa enlightens its subordinates about the very name of the organization. He explains that it refers to "angels" found in Buddhist scriptures, and the five signs of their pending demise: garments are soiled, the flowery crown withers, the body's radiance fades, sweat pours from under the arms; every sign is linked to one of the four murders, thus leaving the fifth crime to be committed.

Ranpo refuses to take the case because of Mushitaro Oguri's warning about the fall of the Agency and Fukuzawa reminds him of the Azusa Yumi displayed in the President's office, though calling it a mere piece of wood. According to Fukuzawa, the Agency has to stop the murderer even if it means putting their lives on the line, not because of the award but because of the Agency's morals and values. The President thus lets Ranpo investigate the alleged fall of the Agency while the other members focus on finding the murderer.

After the Agency is falsely incriminated for the murders and is believed by the government to be the Decay of Angels, Fukuzawa is put under arrest and called "an enemy of the state". Right before his arrest, Fukuzawa was giving Mori a phone call and asked for the Port Mafia's protection over the Agency. Mori accepted on one condition: a member of the Agency must transfer to the Port Mafia. Fukuzawa forbade him to choose Yosano as she would not tolerate being Mori's subordinate again. Afterward, Mori lies to the doctor and tells her that Fukuzawa consents to Yosano transferring to the Mafia.

Eleven years ago, Fukuzawa and Mori fought against each other for the guardianship over Yosano who was then a little girl. While Mori wanted to use Yosano's ability in order to seize Port Mafia's leadership, Fukuzawa wished to protect the girl. The battle ended Fukuzawa and Mori's alliance. Ranpo, then the only member of the newly founded Agency, took Yosano away and asks her to join the Agency; according to the young detective, Fukuzawa and Ranpo did not seek her for her ability but for her kindness.

Ōchi Fukuchi, commander of the Hunting Dogs, pays a visit to Fukuzawa while the President in custody under Fukuchi's unit's supervision. The two men are childhood friends and Fukuchi brings sake to drink with Fukuzawa while joyfully chatting about their respective lives and responsibilities. Fukuchi then sternly asks for Fukuzawa's confession in exchange for bringing a halt to the hunt for the Agency members. The President kindly refuses, and Fukuchi suddenly waves his blade only to stop an inch from cutting Fukuzawa's manacles. Indeed, Fukuzawa planned to free himself this way before taking Fukuchi's sword. The commander of the Hunting Dogs then praises the President's swordsmanship, wondering if someone who's able to draw a sword at the speed of sound like Fukuzawa is really human.

When the Hunting Dogs commander tries to bargain over information about Kunikida's whereabouts, Fukuzawa declines the deal once again: he deeply believes that Kunikida is still alive; otherwise he would have felt it. Fukuzawa also has absolute faith in every one of his subordinates and tells Fukuchi that as long one member remains, the Agency will never give up and is bound to win.