I guess this is not that different from the old school "sisters" dynamic (i.e. a very close bond between senpai and kouhai); the younger girl is just even um... younger here. I wonder if there will be any time skips, or if it will lean into the "onee-loli" thing instead.
The crumbs of worldbuilding so far are a good sign, although it's hard to have faith in any series with SFF ambitions surviving long in Yuri Hime. (Some combination of interests from the artists, editors and readers seems to discourage building a supporting cast, and a plot beyond romance and drama. The ones that attempt this don't do very well.) Well, maybe this one will do okay, since it's an adaptation.