Atsu is a junior yakuza member subordinate to a senior figure called "Aniki." His past includes a career as a renowned soccer player, hailed as the "Maradona of Osaka," though specifics of his playing days are not detailed.

Driven by vengeance because Myon's father seduced and eloped with his girlfriend, Atsu aggressively confronts the family at their yakitori restaurant. Physically, he is bald with black eyes. During this encounter, he threatens Myon at gunpoint after her fiancé Ryo intervenes and is knocked unconscious. As Atsu prepares to sexually assault Myon, he shifts focus upon hearing her call Nishi's name. He then kills Nishi by firing a pistol into his anus. Aniki views this act as reckless and lacking control, leading him to execute Atsu for the transgression.

In an altered timeline following Nishi's resurrection via divine intervention, Nishi kills Atsu instead. Aniki subsequently contacts their yakuza boss to report Atsu's death, mentioning his past significance as a national soccer player. An alternative narrative interpretation, termed the "All Just a Dream" theory, suggests the core events are Aniki's imagination while waiting in a car. Within this framework, the story concludes with Atsu failing to board the same train as Myon during a station chase, contrasting the opening scene where he successfully followed her.