well its not hard to see it is AI Generated. every couple pages during the doujin, the art style changes. it's subtle but noticeable if you're looking for it.
like I'd say the easiest way to see it is looking at their hair and seeing all the different ways its drawn, then towards the end when Mei and Shiki have sex, their clothes go from relatively simple in the way its drawn to very detailed for no reason.
I'd willing to forgive shading being slightly different each page if it weren't for the inconsistent line work constantly changing with every panel.