It's the two philosophies of writing a rom-com: (1) becoming a couple is the endpoint to be achieved in the last chapter (with a bonus chapter in the tankobon of the wedding) or (2) the relationship is the point, so how quickly can we get through pairing these people up?
If you have to rush an ending, might as well pack as much plot and character development into it as you can: quantity has a quality all it's own, after all...
I'd guess the big reveal if this were a full series would end up being that Sabbath cares less about the food and wants the demons defeated and humans protected. When he's finally the last demon, the MC would be forced to fight him and Sabbath would turn out to be the only demon "ingredient"...
This author's style seems to be telling a story from the MC's perspective, then reexamining it in the next chapter from the POV of whichever other character was the most involved.
So much of the story is centered on Nanami's weaknesses and Kaoru helping her to overcome them by finding the strength to trust others and to be more confident in herself.
While you can certainly debate how effective it has been and how heavy-handed the author's use of the trope was, I would...
Well, they've already established that cross-dressed Kaoru looks like his mother, so obviously his dad will have memory damage and the only way to calm him down and start helping him to heal will be for Kaoru to impersonate his own mother and flirt with his dad.
If I had to guess—based on many years of anime and manga—only one female student will. She'll be the one who sat atop the food chain of the high school as the strongest fighter, and is madly in love with the MC because either (a) he was the first person in her life to treat her as a girl...