Usa is rapidly becoming my second favorite after Ahko. She knows her behavior is problematic and wants to make sure that the people she's around consent to it. She's probably the most mentally ill of the girlfriends so far. (Iku's a masochist, but doesn't seem like she actually wants to be injured.)
So, uh, if your girl does the same kinds of things Usa does, and she has NOT okayed those things with you beforehand, you really need to sit down and have a serious conversation about boundaries and consent.