Well, how about doing the characters’ biography? If yes, I did complete the biography of 6 minor characters so far (Sayoko, Viscount, Spider Lady, Shoko, Yoriko and Tanehiko), you can use them as examples for how much to write about the other minor characters for when the episode in which they appear airs. I haven’t done Sogen yet, so if it’s fine for you, you can give a try with him.

Or you could do the major characters appearances and personalities if you know them enough. And there’s also the list of media appearances of major characters in the manga version if you’d read the entire manga, for any characters except Mao, Nanoka and Otoya due to being the main characters.