From what I can tell it seems like it’s sort of up to them how much they want to play a character vs streaming as themselves, with the possible exception of the ones whose vtuber identities are the intellectual property of a company that employs them. There’s a spectrum of things like how much they lean into their character lore, do a voice/mannerisms, or how much they use the avatar as a privacy shield and avoid revealing personal details.

Not that there’s anything wrong with it either way, it’s basically similar to pseudonymous internet identities, but for live streamers. Anyway if we’re shilling vtubers I want to shoutout my favorite chicken themed vtuber, Henemimi