Schizo headcanon time!
”It’s random chance” is just a convenient lie told to subjects who haven’t yet realized/won’t admit that the sex change is due to their own desires. The truth is, Richou was always a maiden at heart, she just hadn’t realized it yet, and the lie told here is a way of delicately handling trans people who may not yet have discovered it or are hiding it. Good for her, hope she comes to terms with her own feminity soon!
Anyways I’m headcanoning this solely because the “random chance” thing is way too handwavey. At least make a supernatural event like this a themes and such thing rather than having essentially the equivalent of the author stepping in and saying they just didn’t give thought to it and wanted to skip to writing the story.