Kouichirou Mutou, a Japanese construction worker on a Tokyo stadium project, survives its catastrophic collapse during devastating earthquakes. He navigates the ruined city to reunite with his Filipino wife Mari, their teenage track athlete daughter Ayumu, and younger video game-enthusiast son Go at a designated shrine refuge. Their mixed-cultural background later exposes them to prejudice during their escape.

Kouichirou assumes a protective role, organizing supplies and guiding the group through hazards like flooded streets and unstable structures. He demonstrates practical resourcefulness by killing a boar for food and using colored lights to mark safe paths. He prioritizes family unity, insisting they stay together rather than separate for efficiency during travel. His leadership extends to assisting other survivors encountered along the journey.

Kouichirou dies abruptly in Episode 4 while foraging for food near an abandoned town, stepping on a buried wartime landmine. The blinding detonation kills him instantly. His death occurs without prolonged dramatization, leaving only his wedding ring recovered by Mari. This loss profoundly impacts the family's morale and survival dynamics for subsequent events.