Kenichi knows Furinjin is super strong (she beats his ass in training everyday) yet still has the "I must protect her" attitude. I don't see any new nuance or anything different about this lame trope in the series. It's actually worse because you can't ignore the fact he's jumping in front of her because she's a girl. Early in the series, before he knew, he at least had an excuse. But to hold onto that way of thinking even after learning what a demon she is...Kennichu is one of the better bad examples because the series is self-aware that Myu is actually much stronger than him since she got more talent and a longer history of training, which is actually an important thing for the managa. Jarring fanservice aside, the manga makes a good job having girls not actually be weaker because they are girls. Not even that one Yami master since that one was out of choice.
It's worse when women get degraded into healing or utility positions or to the point where they lack behind so much behind the male characters that they really constantly need help. And then there's of ciurse the category that fights only against other women and get their clothes shred or wet during the fight.
But there are a lot of positive examples of strong, fighting women in anime and those really appeal to me, like Black Lagoon or Gintama.
Fucking laserguided amnesia all the time in all kind of anime. stahp!
I guess if you look at it as his training goal then it somewhat makes sense but it's still pathetic. "I shall train until I've reached demon status so that I can protect this girl who is already fully capable of protecting herself against pretty much anything."
Edit:
The characters aren't forgetting anything. The end of the first season of ai yori has the couple pretty much getting married. Queue the second season and we're back at square one of a harem.
Sword art online second season at times makes it seem as though the couple that spent months together are just pals. Sao isn't as bad as ai yori as at times it seems like they are still a couple and also I can see how moving a virtual relationship to the real world would result in sort of a reset.