Asexuality is a big spectrum. You can be ace and still physically, romantically, intellectually emotionally, etc, attracted to people. And there is even Ace Flux, where your sexual attraction to people fluctuates and changes (dats me fwiw).

So does asexuality mean anything then? I've spent a couple hours reading about it (and the other lesser known sexualities because I'm gay and I figured I should know about the other letters in LGBTQIA), but it seems like a moving target. I get that it is a broad term that is still somewhat specific; for example, I don't get frustrated when people say "citrus" instead of saying something more specific like "orange" or less specific like "fruit", and I know that the things in this grouping share a number of traits. I've had people who call themselves asexual define it much more narrowly than you have though; thus why I am saying it seems to be moving target. That isn't the end of the world. Goths and emos have been doing that for decades.

So yes, Corin is ace and still attracted to Jin.

Fine. I'm just going to read the series like that and forget that u/Salaris said that Corin is asexual. As long as I get to read about this amazing, gay romantic relationship, people can call it whatever they like.

Also, I would argue his attraction to Jin isn't sexual, but romantic/physical/emotional but that's imo.

In the first book, Corin was clearly charmed by Jin and couldn't stop looking at him in various classes or when he ran into him long before he knew anything about him or had spoken a word to him.