Um

u are thinking too deep into this bruh

He is a yokai. Yokai are not even human. Rei literally just said he has a completely different perception of time. Trying to apply normal, human conventions regarding age gaps to this is just going to hurt your brain, man.

You can’t be serious

If rei had the mind of a child and looked like a child then thats completely normal if he was a grown man reincarnated as a child now that would be a different story.

AND hes a yokai

hopefully it's the former

Ok sorrie guys (ToT) it just seemed a little weird to meee since rei said that his concept of time is different he thought that it had been days since he saw chi so wouldnt his mindset br one of a child's? It doesnt really make sense

That's because you're applying human logic to his age; maturity can be a much more fickle thing in yokai, or not applicable on a 1-to-1 scale. He's a supernatural being, and we don't know shit about his biology or otherwise culturally significant periods of life - if there even are any, as well as if Rei himself has participated in any other societal construction outside of the human one during his stay with Chikage. Biologically speaking, we can't know if Rei has an entirely separate biology as a yokai, or if he is simply magically adjusted to be adjacent to the form he takes (since, yk, horns); in both cases, we'd have to analyze how similar his brain and synapses are to the regular specimen. His mindset can just immediately adjust to the age he makes his body be-- it can be as easy and complicated as that, but we can't analyze that as readers.

By which I mean, this is a really, really complicated issue to actually analyze, especially with how little information we have been given. This is fantasy – quite literally anything goes. It's better to just give it up to your suspension of belief until the narrative makes a comment on this.

Okii thanks for answering d=(^o^)=b