From Attractive Fascinante:

Chiharu and Mahiru, the cute twins, are childhood friends with Akira. Chiharu has decided to protect his “princess” Akira since then. However, Akira became a gorgeous prince when they started high school and somehow, he seems closer to Mahiru instead. After finding out his own feelings, will Chiharu pursue his own happiness or will he give his blessings to Akira and Mahiru?

Note: Very small hinted incest, is never really confirmed, but is in there. Just a warning for people who don't wish to read such subjects.