Yotsuki, a virgin who studied videos and books to successfully have his first sex with his new girlfriend. Then, the younger sister of J● invited him, saying, 'Want to practice with me?' ...!? He was pushed into kissing and taught how, but the lecture escalated more and more. Completely matured, his sister's body caused him to lose reason, and he eagerly went down on her bare genitals, leading to forbidden sibling sex...!
