>a picture of a womans ass that was drawn as fanservice for why there needs to be sex
Also yes, this is called being a male and why giant-ass industry of doujins exists. Men looking at nice character ass and looking for natural continuation, sex, in doujins and the like - is normal. Masturbating - is normal. Am I supposed to be ashamed that my PP gets hard when I see naked Seras ass? Should I be apologizing?
Of course not. Such expectations are healthy and normal for males. If there's a heinous enemy - the story is expected to deliver him to justice. If there's a mystery - it's expected to be unveiled. An unexplored ruin - explored. A nice piece of scantily-clad orbiting love interest - is expected to be fucked by protagonist.
You can do nothing to convince me that there is anything unnatural at all with these expectations.