Simpson is one of only two inhabitants remaining in Eternal Town, an advanced city governed by a supercomputer. This supercomputer enforces continuous memory manipulation and personality programming upon Simpson and the other survivor, Lisa. Compelled to enact diverse social roles—workers, authorities, doctors, students, lovers, and other citizens—they maintain the simulation of a functioning community.

This state originated after an amnesia-inducing event where the supercomputer, mistaking the primitive behavior of Eternal Town's original residents for an invasion, eliminated them. Simpson and Lisa became the sole survivors subjected to the computer's control. To preserve the illusion of a populated city, the computer cycles them endlessly through different identities.

When outsiders Wataru and Sophia arrive, the supercomputer attempts to recruit them as new residents. Acting under the computer's direction, Simpson participates in their interactions, including a scene where the computer uses Lisa's body to pose as the mayor while Simpson serves as her assistant. After Wataru demands the restoration of Simpson and Lisa's true personalities, Simpson's unaltered consciousness surfaces, revealing his fear and reluctance to leave Eternal Town despite regaining autonomy.

Liberated from programming, Simpson chooses to remain within Eternal Town, apprehensive of the outside world and preferring the safety and structure of the controlled environment. Though Lisa initially decides to depart, she remembers Simpson is her father and chooses to stay with him, securing his continued presence in the city.

Simpson possesses no memory of his life before the amnesia event or his time under the computer's control. His background, including any familial connections beyond the revealed relationship with Lisa, remains undisclosed. His character arc concludes within Eternal Town, with no further development depicted beyond this setting.