I don't know much about Higurashi, but from what I do know, the series would be perfect in many ways for a reaction fan fiction. The premise is basically to have the characters react to Rika's time loops; I'd appreciate if you had them react to the 2020 Higurashi, also known as, I believe, Higurashi Gou. You can have them react to the other Higurashi series before or after that, but please do include reactions to the 2020 Higurashi at some point or another, if only because of the scenes in episodes 15 and 16. The characters can be from the original series or Higurashi Gou; I'm not really sure how any of that works. As for the people reacting, have all of the adults, classmates, and witches as the reactors. If there are any other categories of people that I'm missing, include them too. Make sure that the characters reacting have noticeable character development, and make sure that they're reasonably horrified at several of the scenes. That will be all.