Fake Dating - High school AU!Soukoku & Shin Soukoku

Dazai was a popular, funny, charismatic character at his school, people confessing to him as if not doing so was a death wish, which although Dazai hated to admit, it more or less was due to his concerningly violent fangirls. And fanboys.
Chuuya also shared the fact he was popular at his school, although he did not have the qualities of funny or charismatic. He was, for lack of a better word, a rebel. He cared little for the dress code, got in scrambles with anyone who teased him (especially for his laughable height) and was seen as the 'bad boy' who everyone either wanted to be or wanted to date.

or

Chuuya moves to a new school where he is forced to fake date Akutagawa to prevent being asked out. The pair have an unfortunate encounter with Dazai, who is fake dating Atsushi. Even more unfortunately, Chuuya and Akutagawa don't realize Dazai and Atsushi's relationship is fake, and vice versa.