why, i can see this happening they are both servants, both mostly spend their time alone or at their master's side, Youmu aspire to be good companion and attendant, she might have idealized mature and powerful Ran as example, and Ran seem like loving and caring figure, and while she can't love Chen romantically, because she is more of a child to her, she could see and accept youmu's dependency on her. it's a pretty good basis for QUALITY yuri story, actually.
