From Chibi Manga:

She was her best friend and he was her first love...she didn't plan to change that. Ayu and Kaho were friends since kindergarten. They were the exact opposite; and even if both them were cute, they hated men. But one day, Kaho found someone she loved. "why? I was the one in your heart before..."
"Let's play at football" said a boy that Ayu never saw before. But, she felt her heart beating so fast and hurting so hard. It was the beginning of her first love...