This manga is a "turn brain off" battle shounen (or log-wielding action, as the Japanese fans call) horror manga with too much graphic content to be consider as a proper one -therefore seinen-.
The premise and backstory are honestly pretty interesting overall, the execution tho... I have the impression it is made in a so-bad-is-good way on purpose all the way, especially considering how the "anime adaptation" was made with the help of the author himself (and how he pokes fun of his own absurdiness here and there). It isn't meant for us to take too seriously, albeit the characters are doing so in their own way. It's just a quite fun addicting ride full of memes and cool horror imagery. That's the reason why is popular and has a dedicated cult following in Japan at the very least.
If you are here to any sort of complex and well developed plot and characters, you are reading this series wrong, and should just stay away from it as it isn't for you. Anybody else will likely just have a blast with just how crazy and unbelievably ridiculous (not to call just straight stupid, as there is some evident self-awareness in regards to a lot of things in this, if you look at it with other eyes) this series gets.
This is some of the most entertaining page-turner horror manga I've read in a very long time (since my Junji Ito marathon period), even if I also mock some very dumb things that happen in a certain arc to this very day (as they kinda keep coming up again later on).
There's a good reason this manga has a very specific niche and audience that likes it to the point of consistently buying it for more than a decade (we are at 70 manga volumes atm, likely the biggest long-running horror manga in Japan if you not count JoJo as one). If you are not part of it, just drop it, there's no need to go out of your way to express how bad you think a manga that clearly seems made to be a "so bad is good" title actually is lol