From Chibi Manga:

Kaji, Yuzuha's unrequited love, is a good friend of her twin brother Suguru. He's the same age but goes to a different school and since elementary school, he's been going in and out of Yuzuha's home. She's been in love with him all this time, but can't make a serious face when around Kaji. Now they both change to the same high school and there's the chance to decrease the distance between Kaji and her...?!