Game demo, Papa no Iu Koto o Kikinasai!

Segawa Yuuta is a university first year student who was looked after by his older sister, Yuri, but decided to live alone when Yuri got married. One day, Yuuta is asked by Yuri and her husband to babysit their children, Takanashi Sora, Miu and Hina, while they go on a trip. However, during this time, the plane Yuri and her husband are riding crashes and they are both reported missing. In order to prevent the girls from being separated from each other, Yuuta takes it upon himself to look after the girls in his small dormitory apartment. Thus begins Yuuta's life of sharing his everyday life with three girls.

[From Wikipedia]