Ichiro is a member of the privileged Hosino Tribe of cockroaches living in a human apartment. His family holds high status, his father ranking among the tribe's wealthiest and most influential, leading to Ichiro's initial complacency and lack of essential cockroach survival skills, including flight. He is engaged to Naomi at the story's start.

Their relationship strains due to Naomi's dissatisfaction with his perceived lack of excitement and her subsequent attraction to Hans, a militaristic cockroach from another tribe. Despite Naomi's infidelity and temporary disappearance with Hans, Ichiro remains devoted. He accepts her unexplained return and proceeds with their wedding, demonstrating loyalty and a desire for stability.

The Hosino Tribe's peace shatters when the human inhabitants begin extermination. During the crisis, elders reveal to Ichiro that their perceived safety was a falsehood; the tribe leader fabricated stories of negotiation with the human, Saito, whose past tolerance stemmed solely from apathy after his family left, not from any pact. This revelation forces Ichiro to confront the harsh reality of their human dependence and fragile peace.

Facing genocide, Ichiro sheds his complacency, actively participating in the desperate survival struggle. He learns vital foraging and evasion techniques from the elders and crucially overcomes his limitation, gaining the ability to fly—symbolizing his adaptation and newfound determination. His relationship with Hans evolves from rivalry into a tense alliance forged by the conflict with humans. Both aware of their shared connection to Naomi, they agree to resolve personal differences after the battle.

Ichiro's flight during the escape represents his peak development. He is killed when Saito shoots him down using an airsoft gun. Despite his death, his legacy continues through Naomi's offspring; some of her children bear his physical resemblance, confirming his genetic contribution.