Curate, connect, and discover
I'm stupid attached to Grimmchild despite them not really being a character, S rank charm purely on the ability to have a companion. Grown Grimmchild is often depicted as a tiny Grimm but personally, I think teen (preteen? can bugs even be teens?) Grimmchild would be much less put together than their predecessor, acting similair to a seagull, picking fights and stealing from creatures much larger than them, and because of said attitude would not wrap their wings up like a cloak.
I also refuse to believe that Ghost would ever grow to THKS's size, ghost is a tiny bastard and will remain that way. If they ever got the chance to grow up they'd be pk-sized at most.