Mama Sis ~Okaa-san to Watashi, Docchi ga Ii no?~

The hero's father owns an inn named YAYOI. His mother has died ten years prior. Mirei Yasoshima, a friend of the hero's father comes over to take care of the hero. Sometimes she will bring her two daughters with her, and the group has fun together as he grows up. One day, someone wonders who is a better lover: Mirei or one of her daughters. They ask the hero to help decide.
[Summarized from Getchu]