Forest of the Rabbits, Vol. 1 -

Shunta and Tamaki are one year apart, but they've kept up their friendship even as they attend different schools. Shunta loves to see his friend happy, but one day, he comes across Tamaki crying, and something fundamental changes within him, awakening sexual feelings he doesn't know what to do with.

Shunta realizes that his feelings are not right. They're monstrous. Impure. As the two navigate high school, the lines they cross increase, leaving them to contend with Shunta's growing feelings and Tamaki's own desires.