
I remember dropping this yearrrs ago.. and i understand why. The story is overly confusing and complicated when it really dont need to be. And tbh the mcs past litrally doesnt make sense. Maybe its cuz the translation and the scans but like the most important parts are basically impossible to read. This is deff of is time.... i might try the authors other works.. just to see

Did they not kiss when chi was a child? Ans yokai are like beings that live for 1000s of years no?.. um

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.
PEAKKKK