Shin Gekka Bijin ~Hitori Shizuka

Taiki Uneme takes over his late stepfather's tea ceremony master position and sexual training job. One day, his uncle, Genzo, asks Taiki to train a girl. He goes to Genzo's house and meets Shiori Yachigusa, Taiki's childhood friend. Shiori tells him of the disappearance of her parents after they went bankrupt, and now she has to shoulder their debt. Her guardian directs her to meet Taiki.
Taiki is disgusted to hear this, yet he feels some weird, spiritual evolution at the same time. He starts to train Shiori with Hinano Kuramata, who lives with Taiki.

[From Gamelex]