Overview
It should hardly come as a surprise that there's a lot to critique here, but if I had to hazard a guess as to where you are in your journey, it'd be somewhere between the "imitation" and "understanding" phases. You show potential as an artist (even outside the Kishimoto style) and I could see it working out for you, however your execution of these understandings you have of WHY manga works is severely lacking and I hope I can explain these in a way that will encourage you to improve rather than dissuading you from doing what you clearly love.
Art
As you said, you had to relearn how to draw so the artwork being rough is understandable. However speaking on an objective level, it's subpar and no amount of "it's my style" crap will change that. Your character drawings are often ill-proportioned, inconsistent, lack weight, and lack depth. This is why most artists will spend a lot of time making in-depth character sheets for their own reference, from many angles with many perspectives, to keep their drawings as consistent from panel to panel as they can (or so that they can have their assistant monkeys reference them).
The next biggest issue with the art would have to be the constant use of angles, even where they otherwise wouldn't belong. In most cases, this applies to faces, creating uncanny expressions that at best can seem funny, but at worst can appear uncomfortably strange. If you were to begin anywhere with improving, it would be by practicing your human characters in motionless poses, trying to understand what makes a good portrait. While detailed drawings may seem antithetical to the often more simplistic character art of manga, mangakas that can draw characters well can do so because they have the artistic knowledge that allows them to simplify otherwise complex ideas.
Story
Solid ideas, iffy execution. It's clear at least that you have more than just an idea of what kind of world you're building and what kind of story is being conveyed in this world. However, what's clear to you is not often clear to the average reader. Your storytelling is lacking in the solid hooks, bait, and momentum needed to properly reel in the readers. The first half of the story presents far too many unknowns concerning the world, the characters, and plot. We have no idea what he's doing, why he's doing it, or where the story is going other than where the following plot needs to have happen. The initial impression phase is a key moment in hooking readers. In most stories, that phase occurs during the first two scenes where a story will demonstrate to the reader what kind of story it is, what kind of ride it's taking you on, or the general tone of the story. In this case, from my impressions, it was a whiny, possibly schizophrenic guy, talking to his friend; then followed by a monster attacking for an unknown reason with the schizo pissing himself over while carrying some measure of dissonant nonchalance.
Again, while you as the writer might have every idea of what's going on and why, the reader does not. It's the job of the storyteller to understand what information to feed and when to have their readers properly understand the story. Proper usage of this skill also helps build on things like tone, themes, humor, intrigue, and above all else, interest. A bad story told in a good way will always be more interesting than a good story told in a bad way. The best way to build that skill is to just tell more stories. Real stories, bullshit stories, short stories, anecdotes, whatever the hell you can come up with. Gauge people's interest, their reactions, learn when you're dragging on, learn when you telling too much or not enough. With it in practice, you'll be able to instinctively know what bits the audience needs, what the audience wants, and when and where the give them.
Characters
This is an instance where the execution was almost solid. There were a few hiccups with Ryuma, however. When meeting new people, or seeing new characters, humans instinctively try to figure them out. What kind of person they are, what they're capable of, and whether or not it would be hazardous to your well-being to associate with them. So every bit we learn about them, builds on our internalized idea of who they are and it does so in sequence which causes problems if there are things that seemingly contradict each other. In Ryuma's case, it's a guy that's overly concerned about the peace, but then runs scared when that peace is broken, then a guy that's scared but then casually drags his friend's broken body down the street. The idea of the initial impression phase applies to characters as well and within the first two scenes you have traits that conflict with each other unless you know from the start what kind of person he is.
The other characters are serviceable with you successfully imparting the feeling of them having history with each other, but the reader knows less about them than Ryuma. The other "hero" is a good example of how not knowing dick about someone can affect how we interpret the issue. Ryuma says that he has to get to class and for all the reader knows, he picks a fight with some random prick, and then walks away. Even later when they put together that the replacement hero was him, he's still just some random prick to the reader.
Readability + Paneling
Readability is more than a meme phrase used to shit on nu-HxH. It relates to our ability to understand the situation we're viewing in an appropriate amount of time. However, this isn't usually the responsibility of the reader to be perceptive, but rather the artist to cleanly illustrate the scene with minimal noise, proper perspectives, and appropriate effect to things of importance. The BEST example in your own story is the spread on page 51-52 where the object of importance takes precedence over everything else on the page. Our eyes are drawn to it. A more practiced artist might even say that readability is an artist's skill to control where the reader is looking.
The issues from poor paneling stem from issues with readability. The most important thing to think about with panels is not them being boxes for art, but rather windows of context. The beats of the story continue in-between panels and panels are the beats that we as the readers see. Thus, it's important for you understand the panel to panel flow, how many beats the reader is missing between panels, and which beats are of the upmost importance to show. For both of these, I would happily point you to Oda's early work including early One Piece where the illustrations are as crisp and clean as they come, giving you a clear understanding of the scene. He's also quite skilled at panel to panel flow. If you aren't already, head back to /a/ and check out the currently active Wanted thread. It's a series of short stories (which they are far from perfect), but demonstrate the skill he had with readability back in the day. In your story, the art can be a chore to understand between missing beats, an improperly sized panel, or just broken flow.
Grammar
lol
lmao, even
Surely you have some English-native friends that might proofread for you, right? If nothing else, read more English literature as manga can be questionable for teaching English between ESLs translating them, MTLs, and compromises being made for Japanese expressions and puns. Nothing to do here but learn.
The Good
Despite the harsh words, I don't hate it. The ideas and presentation of them almost make up for the negatives. It's easy to see that you're a bundle of good ideas without any existing skill to execute them. The good news for you though is that a mangaka could never make it without good ideas to start with. You see it all the time at one-shot competitions where a clearly skilled artist wants to show off how great they are, but the one-shot they write ends up being a one-shit because they have fuck-all for creative ideas outside of pretty pictures. There's potential here, but it's entirely on you whether you want to grind your knuckles as much as it takes to see that potential through.