The dynamic between Atsushi and Kyoka was changed to focus on Atsushi's psychological growth. An idea not present in the film was to have the reanimated mafia member Sakunosuke Oda save Atsushi from an unknown danger. Asagiri said that throughout the film, Atsushi stays true to his original persona of a weak and relatable person, despite having scenes showing his inner strength. In the Japanese anime and film, Atsushi is voiced by actor Yūto Uemura. Uemura said that while his character initially cannot stand by himself, he appears to become stronger as the series progresses. According to the voice actor, a major impact on Atsushi's development is how he finds Kyoka, wishes to protect her from a dark fate, and becomes a stronger person for doing so. Uemura liked the scene in which Atsushi encounters Akutagawa in the airship Moby Dick, where the actor tried to show Atsushi's strength of will in contesting with Akutagawa. Despite having difficulty in showing the character's strength, Uemura believed some lines Atsushi has when interacting with people from the Guild gave a good impression of his power. Upon first hearing Uemura, the manga and anime staff were surprised by his performance and regarded him as fit for playing the character. In the making of the film "Dead Apple", Uemura felt honored to keep playing Atsushi, mainly due to the character's importance and his impact on his career. When the series is dubbed in English, Atsushi is voiced by American voice actor Max Mittelman. Atsushi first appears in the manga as an abandoned orphan who usually is eager to rob the next person he sees in order to survive. When he saves detective Osamu Dazai from drowning, Dazai is angered because he was attempting suicide. After inviting him to eat at a restaurant, Dazai realizes that Atsushi is a weretiger and asks him to work at his Armed Detective Agency. Atsushi accepts and meets other members who also possess supernatural powers. He also learns he is the target of the Port Mafia, who seek him in his tiger form. During an encounter with the young mafia assassin Kyoka Izumi, Atsushi becomes concerned that she is forced to kill and wishes to give her a better life. As a result, the leader of the detective agency, Yukichi Fukuzawa, recruits her, and Dazai puts Kyoka under Atsushi's care in the apartment he has provided for them.