Ok, the idea is very interesting, but it is poorly implemented, do not be discouraged author, you said that you accept constructive criticism and this has every intention of being so, this can be improved, continue with the story, improve with practice and keep in mind what I tell you for your next FF. I clarify, I have not read all nor do I plan to do so, because I really cannot accept some of the author's decisions, I will talk about them later, but in view of the potential of this idea I decided to leave the problems that I see, with the intention that the author improve and, perhaps in the future, rewrite this story with greater coherence; In the same way, I am not going to talk about spelling because, not being a native, I could easily make a mistake.
Now, it is understandable that the beginning is a bit forced, with the mixture of worlds and everything, but the writing in general is quite rough, the narration does not feel fluid, making it difficult to immerse ourself in the story, I mean, do not throw the information at us so in our faces, also sometimes it seems that you forgot to put something in or it occurred to you later, so you decide to include it as if it were a last minute addition to the plot, like the blacksmith; or I also just read that after killing the bear, the teacher deduced that it was by a sword technique, but that's said by the omniscient narrator in the crudest possible way, you could have done a little scene of Koushirou bending down and checking the cut and then being surprised at the mastery of the sword, internal chatter and all, or something like that ... My point is that is better if you don't throw us the conclusions you want us to draw, use your characters to form the idea little by little or give us the clues so that we can achieve it, the first one is very important to create the framework for the other characters skills, and for giving mysticism.
Another error that I saw is how you attacked the scale of power and the physical reality of things, that is, the techniques that the MC would know do not make sense, some because they require advanced knowledge that he simply does not have or because Zoro creates them on his journey; and, at the same time, doing it like this you just delegitimized all the efforts of the rest of the swordsman in your fiction, wich make it pointless unless this is one of those lame FF of OP characters that act like chinese Young Masters; and the blacksmith thing destroy the logic of your story! It's the reason why DXD is an absolute joke, there's no effort in half of their characters; which brings me to the last and worst mistake, empathy, you tried to make us empathize with the main character through a traumatic past, and it was not that bad, crude, yes, but the idea was there, but there was no growth period or anything, you didn't give us time to appreciate his situation and growth, preventing a true empathy with your character.
And let's not even talk about the casual modifications to the time line, that some do it in series like Naruto, Fairy Tail or DB where the time line is poorly planned and as long as you keep certain immovable nodes everything works, it can work, just if they keep it in a decent explanatory order, but in a story like One Piece where the attention to detail is so high? It doesn't make sense, and it's too big a risk for the mere convenience of your wishes author.
In any case, in summary: Narrative, character development, balance, and be coherent with the origin story and the theme of your novel.
