She is Mine(2009)

She is Mine

It's a love triangle between 2 friends Ryotaro & Haru and Mirei the girl. They are all 15 years old and entering high school. The two boys run into Mirei outside of school and are both mesmerized by her. They then find out she is in their class. Mirei turns out to have "experience" in love matters, while the two guys are completely innocent.