Nevermore (Echoes Book 1)

Does it matter if it's harem or monoromance? For harem: Nevermore by Chase Kilgore. Only the first book is out, so things may change, but despite the blurb, the protagonist is more of a slightly reluctant superhero thanks to the apocalyptic stakes and his backstory. Villain for Hire by Jay Aury is a comedy/action/romance series. It's generally light hearted and happy to embrace the campy side of superhero settings, but generally does a good job of balancing out into fun adventures. Monoromance: Need to do some more looking, and there's no audiobook, but my Magic, Machines, and Machinations is a supervillain romance series. The protagonists more anti-heroes or anti-villains, depending on your perspective, but they're professional criminals who clash with straight up superheroes.