Ohoshisama ni Onegai!(1999)

As a child, Sasahara Tomo has always been "one of the guys," hanging out and rough-housing. Even though, she secretly wished to be a girl instead when she enters elementary school, she keeps her facade, too embarrassed to admit it. But when her love confession was later rejected because she didn't seem like a girl, Tomo was ready for a new start. And how lucky that she's about to enter high school. She's excited. A whole school where nobody knew her! But not quite. There's Shimazaki Akira, who had been her next-door neighbor until 5 years ago.. and it seems as if their "sibling" regard for each other is growing into something more.. But there are problems abroad.. because this is a forbidden love.. because he is her 23-year-old class advisor.