Tsubomi, who is much older, returns home after a long absence and forcefully invites her student brother to bathe together, still treating him like a child. Her affectionate, clingy personality remains unchanged, but now she carries a mature, alluring presence. Saying "You won't be popular if you're not clean," she kindly takes care of him, meticulously pulling back the foreskin and washing even the most sensitive parts. However, upon seeing her brother's penis after so long, she's surprised by how much it's grown—large and hard. Despite her shock, she begins washing it with a lewd gaze, giving him a handjob under the guise of cleaning. Overwhelmed by her tenderness and dominance, he suddenly erupts in a powerful ejaculation. The warmth of their reunion, combined with his matured body and overflowing manhood, ignites an uncontrollable desire, pushing their sibling bond beyond its limits. This work portrays the erotic tension drawn from their age gap and the boy's physical transformation, creating an intimate, sensual relationship. A passionate love story of siblings crossing the line, highlighting the sister's nurturing strength and the boy's coming-of-age.