Seems less rushed when you consider that maybe the author just feels like ending it in an arc or two. Don't see the reason, but is a possibility maybe? I don't know, Rin and Kurohime being the endgame sounds fine (i want more though)
Finished it thinking that eventually it would become something somewhat interesting because of the premise, but it's just otome isekai slop. The heated discussion above is more interesting, i genuinely envy you people for being able to enjoy it.