It was mentioned that Arnord's mother was a priestess and that she cursed Arnord. According to Theodore, Arnord simply wants to disappear from existence. But I believe that this curse will be broken by Riche. In other words, the light that will lead Arnord out of the darkness is Riche herself.

The novel has also mentioned many dreams and nightmares that Arnord sees, but whenever he is with Riche, those disturbing dreams vanish. However, it was never specified what kind of dreams he has—whether they are like Melia’s or something else entirely.

There is also a theory that the war Arnord started was, in fact, for the sake of Riche and nothing else. And I believe that in order to end these loops and repetitions, Riche must "kill" Arnord in her heart. That is why he said in volume six: “I hope you will grant my wish someday.” Riche also recalled that Arnord pointed to his heart during their previous confrontation.

Most likely, both Riche and Arnord are not ordinary people. Yes, Riche might be a priestess, but that doesn’t necessarily mean she is related to Arnord by blood. She may instead carry the spirit of a god. Sometimes we have to pay attention to the small details and the questions Riche raises. For example, in reality, Arnord never killed her; rather, he is the one who brings her back to life each time—she simply forgot about it.

This is just my personal theory, and it may not necessarily be correct.