Trying to use Korean terms in westernized- Euro settings never work for me. Like calling someone Unnie or Oppa always feels soooo strange. But we see it a lot. If it was like Stereotypical Life of the Reincarnated Lady, I'd be more open to the switching of terms since you not only get a reincarnated-isekai FL but also of the regular isekai (crossing dimensions) from a support character/2nd FL.