Shinji Kanou, a typical university student with a penchant for procrastination and a fondness for his adult material collection, leads a lackluster existence until the arrival of the alluring and well-endowed Yumi Mishima and her family in the apartment upstairs. Through a chance encounter that is both awkward and titillating, Shinji's life takes a sensual turn as he becomes intimately involved with Yumi, evolving into her secret lover. With the unexpected addition of Yumi's identical twin, Nami Ootake, the trio embarks on a steamy journey of passion and secrecy, engaging in a daily routine of erotic escapades concealed from those around them.