To the points you listed:
1/3: I've always thought that the girls falling for the MC so quickly was due to his currently unknown origins. Like it's a side-effect of whatever is going on with that. The feelings aren't fake or forced, they just happen a lot quicker because of it.
2: With how many girls there are and the amount available of time each day, you can only spend so much time with each of them. All of them understand that they have to share the MC though, so it shouldn't be too big a deal to not spend time with every girl every day. Newer girls are of course going to have less time since they only recently get introduced, but they'll get more as the story moves forward.
4: With him being 500 years old doesn't matter. That's applying short-lived race logic onto a long-lived race. Aliza is the same age and in the same boat as the MC. They just work differently.
5: Everything has made sense so far and the story flows well enough.
All-in-all, no real complaints about anything thus far. Keep up the great work!
(Don't worry too much about remaking things.)
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I agree with your points he is a fricken Angel (maybe not pure angel but part Angel either way and raised with the beliefs of the Angels)! Also there is a severe lack of men around these girls so what do you expect to happen when a single male angel is dropped into a girls only school! Of course the girls are going to swarm him not only is he a male he has the perfect body of an Angel! He is the Alpha of all males!
So why do people feel it was too fast? It only made perfect since you put a hot jock into a girls school they will all be fawning over him within a week.
So it's already believable now include that he is an part Angel he is going to exude some aura of authority and we all know girls all love that aura of someone with authority.
So how can anyone feel that it was unbelievable?