So, at first the series has promise, but as the story continues one thing happens over and over that is so bad it breaks my suspension of disbelief. And the author shows they know it's an issue by having an apparition point it out.
Acknowledging a problem doesn't make it okay or good writing, and at this point it has to be intentional. The author is intentionally looking down on the reader.
What's the issue?
The main character, Rei, was betrayed by people he thought were friends. It was so bad he hid in a dungeon for 3 years and planned to never come out. He only decided he wanted to leave because he realized he had a childhood friend to rescue. And he tries to live up to her kindness. But he won't kill.
Not demons, not evil humans; only monsters.
And he literally says, and I quote, "I won't kill humans because they can be redeemed and pay for their sins."
He says this about a man who worked with demons to kill 23 men and help them just about eat the rest of the women and children left in the village.
And in that same quote, he adds, "and I won't kill demons who don't attack humans" when explaining why he didn't kill demons who attacked people and have a mission to kill people.
This is contradictory and so nonsensical I can't believe it wasn't written by the beta version of Chat GPT 0.5. There is no reason for Rei to act like he does or believes this.
The main character is evil. He wants the world to burn. That's the only possible explanation that would make sense. But the author wants us to believe otherwise.
The author, instead of writing a believable level of naivete, decides to lampshade it in such a way that suggests Rei is going to lose big in the future.
IF, and it's a big "IF" Rei loses his childhood friend forever, this story will be rated as a 2 or 3. Otherwise, and in every other circumstance, it gets a 1. This story is an insult to any sane person's intelligence.