On the subject of "companion" characters, there's one particular canon I'm looking at. It's the series Dokidoki Precure, in which the magical girls of the series have fairy partners. The fairies have personalities, can talk, take human form, etc., but they spend most of their time as sidekicks and can't really fight. What's more, they personally turn into the item the girls need to transform, which means without their fairies, the girls can't become magical girls at all.