The issue I have with Tio is not that she is a masochist. I feel the author just got lazy with characterization to the point of not even trying anymore.
When we were first introduced to Tio, she was portrayed as a prim & proper lady and part of an ancient race that was supposedly known for being "noble and honest." She herself also acted rather reserved. Even if you pass that off as being due to the situation (she is in front of the friends of people she killed), none of her behaviour screams bold/playful/outgoing/shameless.
Yet somehow, in the next chapter, this is exactly how she is now portrayed. Even if you argue that getting a rod shoved up her ass awakened her to tendencies she was unaware of, she shouldn't immediate turn into a totally different person like that.
You can't even call this gap moe because even gap moe requires a pre-established persona to compare to, and we haven't seen enough of her yet to even determine what is her default personality!