In most anime/manga you'll often find a character not a part of the main cast that's popular and likeable, has depth and is more or just as interesting as than the main characters.These characters get their own spin offs/shows where they're the protagonists examples are Levi in the manga Attack On Titan Levi Side Story: A Choice With No Regrets(managed to get to 2 OVA), Mavis in Fairy Tail Zero & Mikoto Misaka in the Anime & Manga Spin off A Certain Scientific Rail Gun.
Which are some of the characters you think could get their own anime/manga?