Well, it's... questionable? Technically you're making the game with the option of profitting from it, so... I dunno? I'd be safe and change something about the character so it's "Legally distinct" and all that, but we personally won't bite your head off if you do use pre-existing characters.
Mostly as long as it complies with itch.io's policies as well as that they are "legally distinct" as erron had mentioned, there shouldn't be any issues.
