Sweet Room ~Futari Dake no Himitsu no Amai Kuukan~

Nariyuki is an ordinary uni student living alone. One day, he receives a letter from his younger sister, Yuina, living in the backwoods. She wants to stay at his place for two weeks because she is going to take an entrance exams for the university. They haven't met for six years and all he can remember is her childhood. When they meet, Nariyuki is surprised to see her because she has grown up very cute. They start to live together....