A legendary mercenary once known as LOG KILLER, feared as a living weapon on countless battlefields, arrives in Japan under a new identity: Ryuusei Nogawa. The mission he has accepted is not assassination, espionage, or sabotage, but something far more disorienting for a man who has only ever known war. He must raise a baby. The infant in his care is Hoshina-chan, a lively and mischievous child whose healthy development becomes Nogawa's sole objective. Having spent his entire life in combat zones, Nogawa possesses no knowledge of ordinary routines, peaceful coexistence, or gentle childcare, and he struggles mightily with the day-to-day demands of parenting. His methods, shaped by a lifetime of lethal efficiency, frequently veer toward the extreme. To protect Hoshina-chan from any threat, he eliminates dangers in a manner he considers "legal," applying his battlefield instincts to playground hazards, suspicious strangers, and everyday obstacles. The story unfolds in the microcosm of a small apartment building populated by eccentric residents, where Nogawa is closely monitored by a public security officer named Yonesu, who initially suspects him of plotting terrorism and is baffled to discover the true nature of his mission. Nogawa's journey is one of stark contrast: a man who has taken countless lives must now learn to nurture a single one, navigating trivial crises like feeding, bathing, and soothing a crying baby with the same intensity he once reserved for combat. The narrative balances comedy born from his utter ignorance of civilian life with genuine human drama, exploring themes of redemption, the meaning of a peaceful existence after a life of violence, and the quiet, difficult work of building a family from scratch. As Nogawa fumbles his way through fatherhood, he begins to discover a purpose beyond destruction, all while the world he left behind occasionally threatens to intrude upon the fragile peace he is trying to create.