Yousuke and his sister were orphaned at a young age. Yousuke's sister was adopted ten years before the start of the story, since then, he has been looking for her.
One day Yousuke found the couple that adopted his sister, the problem is that they have two daughters, Ayu and Mayu, both of which were adopted from the same orphanage and are roughly the same age. Both Ayu and Mayu…