Ore to Futago to Natsuyasumi

It's summer break, and Yuji has lots of time available. One day, his cousins, the shy Mana and energetic Rina who are twins, arrive at his home. Apparently, their parents are on the verge of divorce, so the twins have to stay with him temporarily until their family situation settles down.
Their cohabitation begins, and Yuji has to make sure they experience a very enjoyable stay.