Orpheus no Mado

The story begins in Regensburg, Germany in 1903. There is a rumor at the all boy's Catholic S. Sebastian Music Institute that if someone looks through a window in one of the towers known as The Window of Orpheus and sees a beautiful girl through it that they will fall in love with her. This love will only bring pain for it will end up like the tragic Greek myth of Orpheus and Eurydice.

Two of the students—Klaus and Isaac see a girl through the window. Not realizing that she is fellow student, Julius, who was raised to be a boy, things spin out of control and their lives are changed forever.

(Source: Wikipedia)