Seiichi Koshide, a supervisor for foreign technical interns, relocates to the coastal town of Kurosaki with his family under the guise of professional obligations. Publicly, he masquerades as a peacekeeper, mediating clashes between locals and Middle Eastern interns while advocating unity—evident during a tense shaved ice gathering where he discourages discrimination.

Beneath this façade lies a fanatical allegiance to Kuzululu, a Cthulhu-like deity tied to his ancestry as a descendant of ancient fish-people. Orchestrating a spate of grisly murders and disappearances within Housing Complex C, he manipulates distrust between residents to covertly prepare sacrifices for Kuzululu’s resurrection. His veneer of paternal concern cracks early when he savagely assaults a man threatening his daughter, Yuri—an act later revealed as part of his cult’s ruthless elimination of impediments.

In the final arc, Seiichi sheds all pretense, methodically slaughtering tenants and confronting investigators. He fatally stabs Kisou Kobayashi before confronting Kimi, the deity Iyoyoloki Soyohosu, whose unveiling of her true form unravels his schemes. His ritual incomplete, Seiichi and his family are slain by Kimi’s power, their mutilated corpses symbolizing the futility of defying a higher entity.

The Koshide family’s relocation to Kurosaki targeted the sacred site beneath the complex, central to their lineage’s pact with Kuzululu. Unbeknownst to Seiichi, his actions disrupt a time loop maintained by Kimi, culminating in the complex’s decayed state in the present. His unwavering devotion to the cult’s cause supersedes morality and kinship, cementing his legacy as both architect and casualty of his god’s doomed resurgence.