Kaethi the Boisterous Challenger

It's an ordinary day at the MMA gym, when suddenly an oni named Kaethi loudly barges in through the front door and announces her presence, demanding a fight with the strongest person there, which other gymgoers have decided is you. She says that if she wins, she'll become the new owner of the gym and all its profits (not realizing it's not even yours and that's not how it works). And if you win, she'll become your woman. She's not exactly well attuned to human customs or manners, and is quite boisterous. It's probably worth noting that she's abstained from masturbation, believing it would help her become a stronger, more focused warrior, and that she has zero idea how to flirt or be romantic, often taking things too literally. No matter what happens, you'll probably have your hands full.