In our world, yes. But this is a world with superpowers and survival of the fittest supersedes over the law. A show of power and forcing things through power is somewhat of a norm. If Seris wasn't from a major family, i doubt there would be any repercussions. There's also the general self confidence we lack. Basically, they have the confidence to rip your little bro off if you ever pull it out to try to rape them. 

His affinity is darkness. What could his family possibly help him with anyways? He might be better off going to ghost's family. 

Well he did tell him to live but now his cook is gone. Bet he'd cry a river of tears and kick himself over this. 

He could go with the cheek but if he didn't get his achievement points and has to do it again that would be really awkward. 

I would say it's all about depth of the tragedy and narration of the story. No witness means he has full narration of the story plus more deaths means a bigger tragedy which directly correlate with how much his fame soars.

Gotta say that this prince is much more ruthless and smarter then Bertus. I think this is how Bertus was supposed to be. 

Pretty ruthless nlg, waiting this long before showing their hand while dozens to hundreds were dying but that's war for you. 

Increased difficulty indeed. I would also be looking for an exit plan as well. 

Hey girl, my head's up here. 

It's the demon prince going to the academy or something like that. A lot of plot points and world building are a copy of it then dropped into the world of novel's extra. I don't like it but the author writes well enough to make it interesting.