By adult I mean over 18-20 years of age and with adult appearances. Nothing against anime with younger characters, but interested in finding some with older characters.
and act like a child
I don’t really remember any examples of hundreds year old loli vampires that actually act like kids. Shinobu certainly isn’t one. I didn’t include anything like this because OP specifically asks for adult appearances though.
I can’t argue this point or agree with it. I honestly haven’t read or watched enough media with characters like this because it’s not my thing.
I just added that because it fit the earlier duck metaphor. And I’m willing to bet money there are actual characters like that as well.