Personally I divide this manga into 2 parts: the first one being the initial arcs where plot armor is nonexistent and any character could potentially die off, and the second being the latter chapters where the core cast of characters is established and you start to realize that most of them will (probably?) make it. Now typically this type of transition doesn't work, because that lack of plot armor and "danger" is what draws many readers in. However, the author did an adequate job of shifting the stakes, and much of the tension that the reader feels is channeled through their ever-growing attachments to their favorite characters.
Despite it being only 120ish chapters, every notable character was fleshed out nicely in some way, and it never felt like their contribution to the plot was forced or unnecessary (this can be disputed of course). I was particularly impressed and invested in the dynamic between our two mains, Gabimaru and Sagiri. Their platonic relationship is probably the best I've seen in all of anime/manga (the only other one I can think of is Ichigo and Rukia), because their "love" and bond for each other is truly genuine even if there is no romance, and they act exactly like you'd expect good friends to. It's a fresh feeling to his genre as you typically find the protagonist saddled with some sort of love polygon that can often overtake the main plot, but by having him married at the start allows for different conventions and messages to be explored. This dynamic, coupled with the meaningful character arcs of our supporting cast, produce a rich and vibrant experience.
Now all of this isn't to say that the manga is perfect. The word building and "goal" of the antagonists can be difficult to comprehend if you don't have a background in eastern religions or history, and the author could've definitely made the exposition less cumbersome by breaking it up some more. I will, however, cut him some slack because the philosophical context he is working with is naturally convoluted, and it isn't the job of an action manga to deliver a full-fledged lesson on these concepts. Other critiques pertain to the characters that were introduced late into the manga. Without spoiling, their intervention arguably made the plot more complicated and irrational than it needed to be. That said, the ending to this manga wraps up the story nicely (not in a groundbreaking way, just satisfying and bittersweet), and any qualms about those new characters are drowned out by the resolution in my eyes.
In summary, it will be the core cast that will keep you invested in this story. From the badass character designs, to their personal growths and journeys, to their budding camaraderie, to the ultimate result of their drive and purpose. Without a doubt, this is one of the greatest new-gen shounens to hit the shelves, and I higher recommend this work of art to anyone who has an affinity for bizarre settings/inspirations and character-driven battle manga.
