Living together with her sister, unemployed brother-in-law, and younger brother, three months have passed with the sister quietly giving the younger brother a small allowance for helping with housework. One night, seeing the sister comforting her depressed brother-in-law, the younger brother suddenly feels an unexpected arousal. The next morning, while cleaning his room, he realizes his cock is fully erect beneath the blanket. One evening, during a family drinking session, it comes out that the younger brother has been spending huge amounts at hostess clubs. Surprised, the sister jokes, "Huh? You're paying that much? What a waste! Just give that money to me instead, hehe!" Playing along, the brother jokingly proposes a deal. The sister responds, "Hmm? If you're paying, why not? Sure, why not!" Getting into it, they start checking their chemistry, growing increasingly excited until they can't stop themselves. Even as they try to keep it casual, their relationship crosses the line and rapidly escalates. An unexpected story unfolds within daily family life, where bonds and desires intertwine.