Hajime Tanaka, a 24-year-old video game programmer at a mobile development company, possesses a quiet demeanor yet displays obsessive tendencies, especially concerning games focused on collecting rare items.

A childhood trauma deeply shaped him: he used his father's credit card to purchase a rare Donraku eraser for 100,000 yen from an online seller named "ditch-11," only to be swindled and never receive it. His father's reaction caused lasting emotional damage, fostering an aversion to competition and a preference for solitary gaming where his only perceived rival was the game's developer.

As an adult, Tanaka became immersed in the mobile game "Zoological Garden" ("Zooden"), collecting rare animals. His childhood eraser fixation transferred to the game, centering on obtaining an ultra-rare dodo – a creature he associated with his past trauma due to the dodo-shaped eraser involved in the childhood swindle. Over four years, he spent over 5 million yen on "Zooden," but his global ranking remained modest. After finally capturing the dodo, his achievement vanished instantly when taxi driver Hiroshi Odokawa swerved near him, causing Tanaka to drop his phone into a sewer. The shattered device rendered the dodo data irrecoverable.

This loss triggered a complete mental breakdown, compounded the same day by the death of his pet cockatiel, Maru. Convinced Odokawa had ruined his life, Tanaka became unhinged and dedicated himself to vengeance. He obtained a gun, wore a mask, and stalked Odokawa. His pursuit culminated in a parking lot confrontation where he held both Odokawa and the gangster Dobu at gunpoint. During this encounter, the rare Donraku eraser fell from Dobu's pocket, revealing Dobu as "ditch-11," the swindler from Tanaka's childhood. Odokawa further identified Dobu as the top-ranked "Zooden" player who had previously obtained the dodo. In a rage, Tanaka shot Dobu before fleeing the scene.

Following these events, Tanaka recovered from his addiction and returned to his job.