Vicious (слэш)

Midoriya and Bakugou wind up in the very last position either of them thought they'd be in: Hero Partners. It's not fun, but they learn to cope. Their first big assignment together takes them undercover to infiltrate a cult, but the situation turns out far more sinister than they first thought.
(Or: Midoriya and Bakugou pretend to be Fake Married, join a cult, start having sex, and learn not to suck as partners, not necessarily in that order.)