Okaeshi~Beast!!

Mikio is an ordinary uni student. He is kindhearted and attentive to his family. During a summer day, he meets two girls. He doesn't know who they are, but they have a lot of common memories. They say they want to serve under him to repay him for what he did for them. At first, he refuses it, but his older brother accepts it forcibly. But it's too cramped to live with the two of them, so he has to choose one of them. He accepts one girl and the other lives with his brother. There are two weeks left in his summer holiday, and his strange late summer starts...