Mixed feelings. Some interesting concepts but I think the Author fucked around too early causing problems with why the reader was reading in the first place.
Firstly the entire concept of the Koharu was just weird. The more that got explained, the weirder it got. And I get that weird is very opinion-based for good weird or bad weird, and imo this was a bad one. As for why I felt that way, it's because the character has too much fucking stuff going on. In a way she's similar to Kilua's own weird-ass sister with multiple personalities who can also grant wishes with lots of little rules in HxH. But here the stuff the Koharu has just doesn't make much sense. She had the body of a doll/no sense of touch which leaves her paralyzed. She's blind. Also when she speaks she opens people's innermost fears causing their fear to materialize. I mean - that's just a lot to try and accept. And this is all just sort of spewed out in the first chapter. Even when we go back (with this last arc) trying to explain why, it's just fucking weird. I dunno. I'd be okay if she was just blind. Reason being that Koharu ended up revealing she can fly and control her limbs, so she's not truly paralyzed. So if we within like 5 chapters reveal that the character has completely overcome this weakness, without any effort mind you, why even have it in the first place?
The next problem I'd say would be pacing. We aren't given what should be the 'goal' of the manga at the start. It just feels aimless. It's not until literally this final arc that we find out they're suppose to spawn the greatest evil and defeat it otherwise humanity will perish. That's something you should really bring up within the first chapter. I'm not saying you have to do the I wanna be pirate king/hokage/top chef/whatever, to make the series work - I'm just pointing out that you need to have some form of goal in mind from arc to arc. Otherwise back to my original point - WHY is the reader reading? At the end of the first chapters 'arc' Ryunosuke and Koharu become true siblings. But then we're kinda left empty. So then we reveal super secret organization that's EEEVIL. Okay. Then in the next two-three chapters it's revealed "oh well they aren't evil as much as that they want the same thing as the good guys but have different methods trying to become a true human"
But then it's like... okay so you're telling me that there are these Demons who are literally emotionless beings with no personality as the sole villain. The other guys aren't bad they're just wrong. Fantastic.
Writers need to learn that you need a fucking villain, and not just any villain - one who actually has fucking motivation and is a goddamn threat to the main character. Bonus points if said villain is able to act as nearly the polar opposite of the main character - Think Batman (Physically strong) vs the Joker (Mind Games). The Joker is intriguing because of his ability to manipulate Batman, it's not that the Joker can simply 1v1 him. Again not all villains need to be that way, but think of any other series and how strong their villain's character are. Hero Academia is having a long fucking arc ONLY focused on the Villains, and honestly I've hated the main villain for not having this arc earlier in the story.
Now let's back up a little bit Ryunosuke sorta got over his character drama too quickly. Character arc-wise he has very little left to grow. So now things just have to happen. But we already beat off the 'evil organization' so now we're going to explore the good organization. But it's pretty bland. Then we get the girl character who obviously is romance interest trope. Lots of just boring tropes with an overall boring arc where not much happened. Then the combat became forefront with how bland it was going to be. Since there aren't any rules - aside from "keeping you weapon in a shape to be in fight mode" - any fight was - MY WEAPON CAN DO ANYTHING!!!
But it's boring. We don't understand what the characters are and aren't capable of. Look at other battle shounen. Look at something like Jojo/HxH/World Trigger. The fights aren't interesting or complex. Maybe you can argue that the series didn't have enough time to grow, but I'd argue there wasn't much you could do because the writer left it too open.
So yeah. I liked that it was willing to be dark at times. I think a little bit of weird is good.
But man you need to reign it on in and figure out what the fuck you're doing with some of this.
IMO what really killed the series was not making the Villain do something big at the start, which would have forced Ryunosuke to have a goal/character development in mind. (AKA why the reader wants to read your series. Koharu kidnapped or something. Dad super murdered. SOMETHING.)
Then follow that up with ANYTHING BUT the stupid arc we had. It's so boring going to the stale organization where everything is safe and protected. Do something else.