I do think there is one thing to note. "Youkai" is a term that means anything that is not "normal". In other words, literally any non-normal animal or plant being, dead or alive, that you can think of (such as a yeti, a spirit, Loch Ness (if it wasn't a dinosaur), a wyrm), any one at all, is a youkai.
The reason I say this is because it is a term that was created by humans to separate themselves from things that "aren't like us", and in that same sense I'd suspect that some youkai would even consider it a derogatory term, as youkai simply call humans..."humans". Because of this, youkai are probably one of the broadest things in existence, and as such, feeling between them are varied on an incredible scale.
So, regarding the genocide, I'd suspect that youkai would feel more apathetic towards the war itself than the actual casualties. Battles between youkai and humans were almost as frequent as battles between humans and humans as well as youkai and youkai, and they usually had different reasons for doing so, but what makes a war significant is that it justifies any reason youkai would have to hate humans, as it solidifies the fact that humans want youkai gone while youkai are just trying to live their lives.
The reason this is significant is because youkai, on the whole, aren't really close if they aren't of the same race, clan, or species. They're not against each other, but usually they only band together if they have similar goals (such as a distaste for humans). As such, youkai species being extinguished isn't all that displeasing to those that didn't have any ties to said species probably wouldn't really care all too much (depending on their personality and their occupation), but it would amplify any feelings they have about humans.
Then there are the reasons many youkai don't like humans. Humans, to many youkai, are greedy, murderous, selfish, careless, ignorant, are quick to act before thinking, and a bounty of other negative things, especially to youkai. And in many cases they are, especially to youkai. This really epitomizes the phrase, "Humans turn their eyes to what they don't understand." Or maybe the phrase, "Humans are scared of what they don't understand," would be more accurate, as they largely do the things they do, to youkai specifically, because they don't understand them and are afraid of them. We don't take the time to understand and make rash decisions based on what we think we know about them.
Granted, this is mostly general information taken from Science-Fiction, Fantasy, and other things, examinations of what I've found to be the case across the literally millions of youkai-related media (historical and otherwise) out there, so this is not necessarily fact in regards to Youkai Academy.
