Jeeesus, OK, I'll keep this all bookmarked for a rainy day, I'm definitely interested!
Hina always calls her Onee-chan and the twin thing is never said in show I'm PRETTY sure.
Though I haven't read anything yet, looking at fan content it seems that both of them are indeed super popular, which is cool.
https://i.ibb.co/HngtYfT/20240504-020718-imageonline-co-merged-jpg.png
https://youtu.be/qj9p6IFSlnk?si=cZ5L4OPM0TjVjwCD