The Orchard of Stray Sheep

Happiness is an obligation. But then, what gives one the right to be happy?
A small, garden-like Academy stands alone on a secluded island.
Ichirou Yamada has been transferred there to work as a teacher.
He is put in charge of Casserole, a beautiful, young girl who entered the school at the same time.
However, things are not what they seem at this "academy"...