First off, I have a lot of issues in describing and expressing my thoughts about this series. It might feel like there really isn't a plot to this at first, but I would say...it's actually progressive (slowly). I mean there were some moments where I felt like dropping this but in the end I just couldn't but now, I don't have to, because it's pretty decent.
It just loops quite a bit with our MC, Agni/Fire Punch who's always struggling with his identity though. But the actions and the dark ambience is pretty sweet. Now, I kind of look forward to MC's and his thoughts of what actions to take because it's always conflicting and sometimes, it can even flip everything over. Also, all his actions basically also bring up some consequences regardless of what he chose to do so it's fascinating because I feel like this is where the story kicks in.
His relationships with his sister from the introduction is basically his core foundation for the entire series so far even up to where the current chapter is (ch.67) and not something to be underestimated (I guess). I'm still actually looking forward to this series despite the slow progress and I was surprised to hear Viz picking this up but then again after the latest chapters, I feel like it's actually reasonable.
Now tldr: this series is a hit or miss, even if it's a hit, it won't exactly be like an instant, but it'll slowly reel you in. One thing though, you REALLY need a good patience for this series either way. Or you can feel like this is just a cheap mess of action and dark ambience instead.