i've had thoughts about this that i've gone back and forth on. ryu's Boob Condition is very much not meant to be a "normal" thing in the setting and it's not quite as simple as "she just does that"; the initial idea and what i still tend to default to thinking of it is that it's some level of hereditary weirdness, but i've had some other ideas that i might try to flesh out for real in future ryu writings. i really need to write more about her samurai clan. watch this space!