That is the problem. Probably because the chosen ML himself is so problematic that the author either has to introduce male antagonists who are cartoonish worse than manchild ML or the infamous wasted unappreciated better choice 2nd ML whose main purpose is to force ML to become a better lover/boyfriend because his positive existence pose a real threat.
You know by introducing Kahu the author unintentionally demonstrate why Dylan is not a good catch/partner for Charlize.
First of all it is quite bizarre that she ends up with the son of the emperor who made her into a sword suffering for hundreds of years. And second after the successful rebellion when she saw that Dlyan turns his father into the same immortal thing she became so terrified because she knows how horrible it is to be stuck forever as a sword.
And when she wanted to leave Dylan for good and ran away he recaptured her and forces her to stay with him until she reciprocates his love for her...
I don't know about you but that is just too messed up and unhealthy!
Yeah exactly, I mean he was the shadow emperor right? So he probably knew about her being turned into a sword right? And even still he didn’t do anything. I might be mistaken on this part because the emperor killed everyone involved in the process of her turning into a sword but I don’t think he would hide it from his descendants and the future kings. It would kinda make the whole thing pointless lol. Yeah in the it’s sort of the same cycle again. Stockholm syndrome, from what I’m guessing. She has no choice to love him or else he won’t let her go. Common trope which is disappointing.
I mean...him being toxic isn't exactly surprising? I'm not saying its acceptable to be in an unhealthy, possessive relationship like that, however, he is literally a tyrant. He's been introduced as batshit insane from the start. The toxicity is just the cherry on top, compared to his manipulative nature. I'm not happy about how their relationship ends up, but it isn't a surprise.

I think his existence was quite unneccessary. I mean in the novel he is just there and stupidly loyal to FL who doesn't really appreciate that he was the only person who really cares about her and died while trying to find her in the original timeline...
Now I am pissed off... Why even bother introducing him at all???
https://mydramalist.com/discussions/recommendation-forum/37302-cure-for-second-lead-syndrome
https://brideandbreakfast.ph/2020/11/28/lessons-from-second-lead-syndrome/