Ugh Sarai being the one to preach peace to Harrow but then part of her (her very dying breath) being used for evil and to further the cycle of violence. She was the first one to see through Viren, and she could never do anything about it. He held her as she DIED, and then he used her to do evil, in multiple ways. Her dying breath to do the spell to kill Avizandum. And he manipulated Harrow to actually let him do the spell as revenge for her. She was the first one to want to break the cycle, but ended up being used to further it more than almost, if not everything else in history.
AND! Callum also wants to break the cycle of violence, just like his mom. But he does bad things in the name of love like Harrow, just as Viren claims to do as well (Viren, who Callum is repeatedly, gut-punchingly paralleled to). Not to mention how Rayla looks a lot like and is paralleled to Sarai...