I'm Fine with Being the Second Girlfriend.

Kirishima and Hayasaka are two classmates who have a secret relationship in the public eye.

In their school life they act as if they do not know each other, but secretly, there is much more than people can imagine. Both of them get into a relationship that becomes difficult to break and ends up being impure, unhealthy and complicated since the relationship between them was nothing more than a fling that simply generated a love triangle before Kirishima's first love and second love.