Yasuo, a warrior from a militaristic cockroach tribe, battles humans in a neighboring apartment complex, clashing frequently with resident Momoko through raids and retaliatory exterminations. Injured in combat, he is rescued by the Hosino tribe—a pacifist cockroach colony sheltered in the neglected apartment of human Saito. Nursed to health among them, Yasuo kindles a forbidden romance with Naomi, a Hosino member betrothed to Ichiro. The affair ignites tensions, exacerbated by Ichiro’s insecurity over his flightlessness, and challenges the Hosino’s complacency under their fragile, illusory truce with Saito.

Upon returning to his tribe, Yasuo remains linked to Naomi, who eventually joins him. Their bond reflects his hardened philosophy of survival, shaped by perpetual warfare: adaptability and aggression over passive coexistence. When Saito’s partner launches a cleansing campaign against the Hosino, Yasuo’s tribe pivots from opportunistic exploitation to reluctant aid, confronting the severity of their rivals’ plight.

In the climactic human-cockroach conflict, Yasuo is anointed his tribe’s symbolic champion. His demise comes abruptly—crushed by a book dropped by Momoko during battle. Naomi later bears offspring blending Yasuo’s militaristic traits with Ichiro’s diluted Hosino lineage, their mixed heritage embodying resilience and adaptation. Yasuo’s arc traces sacrifice, rivalry, and the fragile balance of survival amid human dominance, his legacy a testament to the evolving strategies of cockroach societies against eradication—a cycle of conflict perpetuated, yet tempered by unforeseen hybrid endurance.