Luna works as a maid at the Shigemori household, a middle-class family whose husband has gone missing. The master of the house, Tadashi, lost his wife at an early age and is gentle and kind, while his eldest son, Tatsuya, neglects work and obsesses over pachinko. The younger son, Makoto, is quiet and introverted. Living among only men, Luna carries out her daily chores while silently enduring the loneliness of living alone. One day, while doing housework, she accidentally discovers Makoto masturbating. Caught in the moment, they end up sleeping together, sparking a new romance. However, their affair is soon exposed by the eldest son Tatsuya, throwing the household into chaos.