Kiss Made No Kyori (Yoshinaga Yuu)

From Chibi Manga:
Kaji, Yuzuha’s unrequited love, is a good friend of her younger twin brother Hayao. He’s the same age but goes to a different school and since theyre in elementary, he’s been going in and out of Yuzuha’s home. She’s been in love with him all the 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…!?