Dark M M Books [best] -

Dark M/M (male/male) books occupy a specialized subgenre of romance defined by morally ambiguous relationships , power imbalances, and intense emotional stakes

Unless you are writing extreme horror erotica (a niche, but valid), avoid: dark m m books

"After his twin brother is murdered, a former assassin infiltrates the gang responsible — only to fall for the sadistic enforcer who pulled the trigger. Now he must decide: avenge his brother, or become the monster's next obsession." Dark M/M (male/male) books occupy a specialized subgenre