Former yakuza boss Hisahide Matsukata, once the feared head of the Onikado-gumi syndicate, has handed over his title and retired to a quiet, solitary life in a traditional Japanese house with a small garden and a beloved bonsai collection. His days are empty and lonely, filled only with the routines of tending plants, watching television, and drinking alone. That peace is shattered when a round, fluffy stray cat wanders into his yard, knocks over a bonsai pot, and refuses to leave. The cat, soon named Nyankichi, is a clever, fearless animal with a talent for mayhem—breaking into the house, stealing food, claiming the best cushions, and ignoring every attempt to be shooed away. Hisahide, a man who once commanded absolute authority, finds himself utterly powerless against this small creature.

The story unfolds as a series of comedic battles for dominance between the rigid, straight-laced former gangster and the free-spirited, unpredictable cat. Nyankichi treats the house as its own territory, and Hisahide’s efforts to establish rules—such as keeping the cat out of the bedroom or off the dining table—consistently fail in humorous ways. The cat’s behavior mirrors real feline antics: climbing curtains, hiding in boxes, darting around at night, and giving its owner a cold, superior stare. Yet beneath the chaos, a tender bond grows. Hisahide begins to worry when Nyankichi is out in the rain, prepares special meals, and reluctantly learns to care for another living being. Key narrative arcs include the naming scene, where Hisahide proposes fierce names like Kurokichi and Torao but the cat only responds to the silly, affectionate Nyankichi; summer episodes featuring fireworks and heatstroke; winter scenes with a kotatsu and shared warmth; and moments of mutual care when either one falls ill. Through the cat, Hisahide reconnects with neighbours, rediscovers joy in small daily events, and slowly sheds his loneliness. The manga balances slapstick comedy with quiet, heartwarming moments, focusing on how a tough, isolated man opens his heart to an animal that gives him a new purpose and a reason to smile each day.