18+ Injoku no Heya

Kazuki, a wealthy young man, yet struck by a terminal illness, lives in his big mansion with numerous female servants. Among them is Nanase, who fell in love with Kazuki. She is trying her best to make him understand the joys of life.

However, ever since Kazuki's sister noticed her feelings, jealousy drives her to discipline Nanase whenever possible in her "torture chamber"...

(Source: AniDB)