Good story writing, but kind of stupid MC.
Unlike most novel where side character got their IQ lower, in this one, the MC IQ got lower instead to get the side character some shine.
The reincarnated trope kind of not work correctly, since the MC IQ reverse back into a kid, and also act like a kid.
It would have been better if the MC start off as a kid instead, and just have some idea that he in an anime work, or die while he still a kid or in sick bed and never experience childhood. Since that way, it feel okay to be a naive.
Another kind of hateful point is similar to other fanfic where the MC train very hard, with his own training arc and stuff, but got BALANCE when fighting real battle. In this fanfic, it not too bad, but we can still feel the nerve a bit.
Another point is, the story is too bland, since it mostly the MC slice of life moment, and it poorly made, since it all build up to a fighting fanfic.
Another point is the sign of something bad happening, it done poorly, those sign should be miss by the MC, but author made the MC aware of it and do nothing about his suspicions . It very frustrating when novel done that, it only make reader complain. It make the MC look dumb/careless. It made the reader feel that the mc should have done better.
Also, I got a feeling that in this fanfic, the MC is not gonna have control over his own destiny, he will always be blackmail or have something holding him back wasting his potential etc type of cliche. The type of cliche where we are given a very promising start, but MC will always face setback that always take something from him for character development.
That why mc shouldn't be a reincarnation in the first place, because reincarnation itself is the biggest setback, and develop the character already. That why reincarnation trope always push out perfect MC which rarely change character, and never naive, at most, they don't have enough information to do much, or else, they will try their best in most case.