Nyuurin ga binkan'na koto ga imouto ni barete waraware nagara sanzan moteasobareru zako chikubi ane: Kasumi Tsukino × Hikaru Minazuki
A younger sister with a small bust discovers that her older, well-endowed sister has extremely sensitive nipples. She bursts into her sister's room while she's secretly masturbating, and licks and sucks them! Her younger sister's tongue skill brings her to orgasm in an instant. As the days go by, the younger sister intensifies her teasing, and the older sister becomes increasingly responsive. In a final twist, the roles reverse, revealing a new dynamic between them...
