Another rather generic manga, the MC is super OP but usually goes Saitama. He gets a bunch of weak to fairly strong companions. But wait! There's more to it.

Once you read to chapter 15 or so, you'll that there's much more to the story. The MC isn't loafing around, he doesn't kill demons not because he's another Emiya Shirou ripoff but he actually has a far more important business to take care of.

Now, when we see those series with level system, classes, attributes, floating menu above characters, the in-series characters take it as a granted never questioning why things are that way. This guy is suspicious of that system, he wants to know how in the blazes this suddenly began, who did this, who made humans and demons fight and more.

This guy realizes that the classes system provides some benefits to each class, he exploits it and reaches Lv.999 (as the titles suggests) and discovers something, a clue to figuring out this world.

I wish that this series would have started a few years earlier and not in this hodgepodge of isekai, reincarnation, magic fantasy era. Then this may have been another Arifureta or perhaps something better. For now the story is still in the starting, the initial 6-7 chapters weren't all that special, so I'll rate it a 7, but I hope that it improves and makes some name in this crowd of mangas.