>>49873097
Her name is actually written as Yuiman Asama (ユイマン・浅間). For whatever reason, ZUN uses western name order for her, like he does for some others.
Her given name is also written in kana, though the name of her homeland and namesake Yuimankoku (維縵国) is written with kanji as normal.

Maybe the name thing is meant to represent how the Lunarians debased her and turned her into their tool, since naming things are established to give you power over them and define their nature, as we also see with Sakuya (who also loosely relates to this game through her famous namesake).