First let's talk about the good parts of the story. The author's grammar is good enough for this site, just some minor mistakes that do not detract you from enjoying this story. The chapters are updated with a decent pace(1-2 per week), with the occasional mini-hiatus of about 3 weeks at the longest. The world background is based on the novel, although the author has taken some liberties here and there that still fit into the original story and its feel pretty well. At the very least, as of chapter 31 there have been no significant changes that makes this story unbelievable.
Now comes the bad portions. The story started off decent, following the novel's storyline and history with a decent pace and no large time skips that would ruin the story's progression. Then the author decided to add some exaggerations here and there, some unexplainable OP healing logic that the MC does not have any prior knowledge for to be justifiable, and the occasional overblown personality of original characters that are fairly noticeable and overall annoying to any reader that has read the entire novel series.
An finally we get to the worst part of this fanfic, as of chapter 31, which is the character design. It looks like the MC's IQ and maturity as someone who is over 20 years old mentally is inversely proportional with his fighting skills....You can't justify the lack of forethought and mindboggling level of cringe/edginess in his thought process or speech just by saying that his pre**** body is affecting his mind or that being a pervert "runs in the family". The level at which this is being shown is unrealistic. I have personally never met anyone over 10 years old who has such an unrealistic view of the world or who hasn't grown out of their chunibyo syndrome at that age. He was born in that world, and yet he is LESS mature than the kids that were never reborn! Heck, if you told me that he has a mental disorder that is limiting him mentally somehow then it would make more sense than whatever dialogue is being shown here. This fanfic started off well enough, with an understandable thought process from the MC, and then as soon as the MC started training or got a girlfriend, it's like he devolved into a glorified primate with an overblown ego the size of Mt Everest. I was never a fan of Rudeus in the novel, but how it THAT clown, who was a former trash NEET with mental scars(if you can even call them that), more mature then someone who was supposedly at least a semi-functioning ***** before dying? Author, please, don't ruin this fanfic with subpar dialogue. A good rule of thumb is, if you can't imagine someone saying something in real life without hiding their face in utter shame, or you saying it in front of a crowd, then it probably shouldn't be written down, otherwise it will degrade your character. Your benchmark is not to be worse than Rudeus, a goal that should be realistically achievable even if you were writing this fanfic drunk, with your feet, after Google translating a non-native speaker 5 times retelling you a cliff notes version of Rudeus's personality.
My recommendation is to fix the MC's personality in the later chapters, if you don't want to change to earlier chapters, or your fanfic will drop faster down the rankings than a boulder falling from the aforementioned Mt Everest.