@Vasqueztion As snakeyes put it, he's powerful enough, the yokai world might actually expect him to have a harem, but human society would not look kindly on the situation, because they're kinda prudes on the whole polygamy situation. The solution would be to have one of the girls be his "legal" wife for the purpose of documentation (in which case, Chisaki, Sagiri, or Hibari would be the optimal choices, since they're likely the only ones with actual, legal existences) and the rest just be "friends" that live with them; after all, they
do live in an old inn that's been converted into a dormitory, so it wouldn't be that strange.