Oh boy one chapter left... I hope there are volume extras
If the story didn't focus on the emotions and human drama, this scenario is a very standard shounen affair, if a little edgy. We were shown one from someone we know to be a good person and had very negative experiences with the environment they grew up in. But how about from a cookie-cutter shounen protag with a very straightforward take? Stop me if you haven't heard this before:
Protagonist lives in a world with monsters
Monsters killed people protagonist cares about
Protagonist grows up wanting to get rid of these monsters
Monsters also turn out to formerly be human, generally against their will. But the monsters shown end up doing bad anyways, so they get killed and die without much introspection. Sometimes there are good ones, but they are shown to be an exception rather than the norm
Monster-itus takes hold of an important character that Protag trusts
Standard:
Protag believes that Important Character is still good, and gets hurt because of it
Dozens of comments saying Protag is a dumbass for believing that Important Character was still trustworthy
Protag goes to kill all the monsters because after his experience, he realizes they can't be redeemed no matter how much they don't want to believe it
But Sauro isn't a shounen protag, and this series is a more nuanced (yeah, I'm surprised I'm using this word to describe a Mochi series too) take, so:
Sauro believes that Arsenio has turned evil, and gets hurt because of it
Understandably, dozens of comments saying Sauro is a dumbass for not believing that Arsenio was still trustworthy
Sauro goes off to kill all the monsters because if he believes that they can be redeemed, he will be crushed by the guilt of what he's done
It's incredible how different the same actions and world are depending on what you see and experience. Is this an allegory for something? Noooooooo, totally not /s