Can Momo not handle the seiza position for too long?
It's hard to do, and you generally have to be used to it not to have your legs fall asleep.
Hence, the "traditionally raised" Hana is perfectly fine with it, as she has lots of practice, and Yuzu is the most "traditionally feminine" of the student council, so they have Momo failing to do Seiza, while Yuzu can.
