Title Mitei no Prologue

In Yuki Nanami's class, a 3rd year high school student, there was a man resembling a saint named Yatamori who exuded an aura that kept people away from him.

One day, Nanami comes across the notebook he usually uses for writing and finds out it contains a novel. Surprised by what he saw, Nanami goes to Yatamori's house to express his feelings, only to discover him in the arms of a man, which makes him look nothing like the saintly image he had of him.

As he was tormented by that scene and couldn't get it out of his mind, Yatamori's asked him to pretend to be his new boyfriend to break up with his previous boyfriend.