itch.io

I know a big part of the questline is under Lina. Looks under her personal quests under the Book Quests section. It might show some red-colored prerequisites you have to do first (I think there is a book quest for Alice and finding a dancing teacher for Lina). Once you get those done, Lina will want some books to read because she is bored. I don't want to spoil the rest but that should put you on the right path. Most of the quest has nothing to do with the anime world. Just keep progressing through the girls' various quest and you should be able to complete it.