It starts out with the main character going on about how powerful he is, how he easily beat all the leaders of the demon army by himself. He could even beat all four of them by himself, he's more powerful than any person or thing on earth, continuous masturbation for the self-insert's ego. It's boring. It makes him joining the demon army pointless, if he wanted to stop the assassins, take over a kingdom, get revenge, he easily could. He's so powerful there's really no reason he would need the weak remnants of the demon army that he singlehandedly defeated to do anything. He just wantsa place to stay and some people to hang out with I guess.

It seems like he's going to be helping the members of the army get better, and make improvements, but there's really nothing interesting about how or why he does it. There's no real reason he needs them, and the way he solves problems is just by being the most powerful character who already learned every secret technique. That's it, there's nothing clever about it, and the four demon lords he's helping are already powerful themselves, just not compared to him.

Then there's some weird pedo shit with an underaged animal girl who wants to marry him, along with some weird choices for angles involving her. It's not as bad as something like mushoku tensei in that regard, but it's still weird. Even if you're not bothered by that it's just boring. I feel no interest in going any further.