Ayumi Kimito, a high school girl, moves in as a lodger at her cousin's older brother's place, where he lives alone. Before long, the two begin cohabiting, and despite realizing it's wrong, they start a romantic relationship. Their forbidden bond brings sweet, warm days filled with dreamlike intimacy. Pure yet bittersweet emotions grow between them, making each day incredibly erotic and deeply affectionate. This work portrays the blissful, sensual cohabitation life of Ayumi and her older brother in vivid, intimate detail.