Spoiler time. So, the MC/OG FL divide is because she thinks he's dead and has "evidence" of it. After their happy times were rudely interrupted by everyone dying it seems she tried to pull that 'protect MC by distancing from him, make him hate her but at least he's safe' shtick and it horribly backfired. From her perspective, all that did was drive MC to a painful death immediately afterwards. Which probably has consequences on the sanity side of things.

On his side, post-timeskip MC still can't handle her seemingly abandoning him right after waking up from a disaster like that, considering his PTSD and trauma and everything. He can't even look in a mirror or interact without a mask on. At the academy he learns she apparently moved on long ago and has been living it up with money, power and a loving fiance she brags about, so now he has a growing grudge on top of a request to support someone opposing her family.

Going by general story trends I'm figuring her mysterious fiance has a good shot at actually being the MC (or his memory, from her point of view). The burnt ring of his will probably come into play somehow. If that is the case, everything she says or does against MC keeps stacking up the drama wagon for whenever it comes out. It's still early in the plot, so I'm hoping the situation drags it out for some time -- the longer this goes unrevealed the worse things will get between them, and the bigger that eventual melodrama will be. It's a guess since there's not much given about her so far, but if she is a villain in this series I think she wants to just watch the world burn now.

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Edit (deeper spoilers) :

Hah! On point with a bunch of the guesswork but it looks like I was off on that last part. The OG FL is being antagonistic & doing everything she's doing because she's on a warpath to purge the ones responsible for the disaster. It's mostly out of revenge but she's also shown a bit of wanting to honor MCs memory by doing good things, like he would have wanted her to. And, we've found out who caused the tragedies! It's the Villainess' family, yes the same one MC is now supporting. She didn't know what they had done, and MC doesn't find out for some time.

Villainess has been corrected, she's fallen hard for MC in no small part because his magical weirdness' influence means she's no longer experiencing the constant magic feedback that was driving her suicidal. They discovered & survived her family's evil scheme together, but likely more drama mounting as she still hasn't made the connection that her family's (evil) plans were what directly lead to MC's situation. Oh, and backstory-FL appears to have caught the scent of MC's true identity.

the MC is well written and has logical personality traits according to what he's been through, his sometimes overly violent tendencies are the only somewhat ungrounded thing but it could be an inherent nature of his.

The first FMC is also more or less logically written, from her being an arrogant spoiled child to the sweet MC's partner, and even though many don't like how she pushed him off after they survived the village attack, I also see that as a rational conclusion a troubled young girl could have come up with after barely escaping death with the MC and returning back to her family only to be constantly hunted by assassins, in that state of mind and fearing for him, although it was a harsh decision for the mentally fragile MC that had just lost everything, it's not completely nonsensical, but I don't like how her character turned out at the academy, her making a facade and engaging in the nobles politics is fine, but after finding out who the MC is, her subtle changes and not so eager moves to reclaim their relationship felt lukewarm to me, I think she should have made more desperate moves and tried to get back to him with whatever means necessary given the obsessive relationship painted between them even if she wanted him to gradually accept her again, because that's how they were initially set up.

The second FMC however for me is a perfect example of great character development, she started off as the arrogant spoiled young lady type with a good reason for how she overly did it, and turned into a warm doting tsundere that doesn't like to show it but is overly reliant and clingy to the MC.

minha Yeon is a useless brat who one sidedly gets saved by the MC, putting the MC in life threatening danger and cutting his life span short. Doesn't even think of how she can help him despite all he did for her, And while the MC is constantly thinking about serious things like how to help her and how to protect her she's off in la-la-land thinking "oh he's so handsome" and "wow he's so great how can I seduce him". And when she does attempt to make a move all she does is just borderline sexually harass him and then get mad at him acting like he's the pe*vert. Not only that her personality is worse than 12 year old seoyeon's personality as a 17 year old. At least 12 year old seoyeon was just like a cute childish brat, she even forgave the MC for beating her to a pulp. While Yeon minha still acts worse than a 12 year old at 17 and its just plain embarrassing.

I really liked the first few chapters, for Seoyeon and Hyun's relationship you can really see the chemistry between them as they grow up together. Even tho they were brats to each other you can see how they both change for the better for each other. And despite the fact that she did hurt him horribly, she only ever did it because she cares about him and wanted to protect him. Everything she in her life, even after he died was his sake (her basically dedicating her life to avenge him). In comparison what even is there between MC and minha.

i know im repeating myself here but all minha does is take take take and act like a brat. She hasn't made a single bit of effort to help him and her character hasn't developed at all. SHE HAS NOT DONE ONE THING TO HELP HIM. She is just as horrible a person as when she first met the MC and correct me if I'm wrong, she hasn't even apologized for being such a bootycheeks person to him in the beginning. So like the audacity to like him is crazy like she does not even deserve to like him.

after reading a bit more I hate her even more. Ok I admit that she does some things for him, like straightening his tie, or wiping his body with a towel. Both things that he can easily already do himself??? And it's just her being a pe*vert taking advantage if doing "favours". AND THEN AFTER LITERALY JUST STRAITENING HIS TIE SHE THINKS "oh he needs me" LIKE SHE LITERALLY DID THE EASIEST BARE MINIMUM THING EVER AND IS LIKE "HE NEEDS ME" and her audacity to think that him helping her is to be expected despite the fact that SHE HAS DONE NOTHING for him. I CANT EMPHASIZE ENOUGH THERE HAS NOT BEEN A SINGLE TIME WHERE SHE THOUGHT ABOUT WAY SHE CAN HELP HIM.

The story phrases her dependence on him as like something cute/quirky but it's not at all. Maybe if he depended on her just as much. But no, he is not into her, it's just her one sidedly pushing her feelings onto him and depending on him. It's like emotional blackmail at this point. Like they even pointed it out when he stayed at the commander's families house that he realized that he needs to be her anchor or else she'd have nothing to live for.

Essentially, Minha is just seoyeon but worse in EVERY SINGLE ASPECT. Every time I read a scene of her my blood boils. I almost quit reading because of her. I'm so glad Jin seo is shaping up to be another harem member because that means I don't have to see Minha's annoying face