After taking a gap year, Kiyoshi Naoto finally gets into a university in Tokyo and moves in with his older cousin, Luna, whom he has admired since childhood. But when he arrives, he finds that Luna has transformed from the gentle, clean-cut girl he remembered into a silver-haired, pierced, and scantily clad woman whose apartment is a mess. Worse, every night he hears scandalous moans coming from her room, leading him to suspect she is bringing home different men. Naoto is constantly flustered by Luna's close physical proximity and ambiguous behavior, while she seems to enjoy teasing him. At university, he meets the seemingly kind and helpful Kawashina, who offers advice about his sleepless nights, but after a drinking party she reveals a hidden sadistic side—she has an obsessive urge to bite him, stemming from a childhood encounter when she left a bite mark on his back. Meanwhile, Luna's friend Ishikari Hiba arrives and subjects Naoto to aggressive, sexually charged questioning, adding to his confusion. As Naoto struggles with his lingering feelings for Luna and the chaos of the quirky women around him, the central mystery of the nightly moans is eventually resolved: Luna has been masturbating while watching adult videos with her earphones not properly connected, and her actions are driven by her own long-held desire for Naoto. A childhood promise of a kiss when they grew up further complicates their relationship. The story is an ongoing comedic ecchi romantic comedy centered on Naoto's tumultuous new life surrounded by older women with strong, unconventional personalities.