I don’t judge but the author who made Manerkol a RO has no room to be confused by people who want Mornie, that’s essential the same logic for both.
Maybe I’m in the minority here but the anime stuff is something I quite liked, some of the best in the books were basically anime episodes in novel form.
Falco/Flynn (AMR). Not sure if they are universally hated but there is always someone wanting to punch them, as it seems. I mean, they’re indeed annoying and very punchable, but also pretty funny/cute when embarrassed
I love Falco and all his grumpiness!
Falco is the annoying little brother you got stuck with that grows on you over time. Also, I keep thinking of Attack on Titan because of his name.
+1 for Leon, Manerkol and Jun/ko
My reasoning would be that the context of their relationship with the MC is interesting. You don’t quite know where it would go based on the story in comparison to the people that are on MC’s side.
For the more morally questionable ROs, it feels cathartic. They do what they want and are wholly selfish. But knowing that someone that is just so self-serving, want MC in their lives and warp their plans due to them, can create a sense of validation. For Jun/ko MC is basically their world which also creates that thought that you are unconditionally valued. The feeling of being special in the relationship is more intense than what would be established with one of the healthier ROs.
I really love Leon!
When I first played A Mage Reborn, I read a few pages, decided to play and then I read the RO description, when I saw Leon, I thought “Holy shit this is the king who excuted me!” I decied to romance him immediately because I love the romance that is dramatic and spicy!
And I played as a very noble and kind MC, so the fact Leon failed me means he failed love, friendship and chivalry, and every moment I think about this give me a lof fun.
Did Strephon from Empyrean shoot me off a cliff? Yes but at least he had the decency to give me great bathroom sex after the fact.
No matter how hard I try, my characters always turn Peter Pettigrew real quick when Manerkol breathes their way.
I don’t know 
He’s cute but it kind went up in flames 
Hehe
“Lady Argent” from FH(Retribution).
I think she has got some attitude problems but I always fall for ‘Haters turned lovers’.
I thought everyone loved her??
Or I might just be looking in the wrong places, but I always felt a little out of place for wanting nothing from her other than distance lol
I definitely would not describe her as hated or controversial
I’m gonna pass too since I get the sense that she’s one bad day from taking my head off (which one could be a coin toss), but a lot of people are apparently all for her. I guess she’s in the sweet spot of “somewhat unstable, but not crazy enough to not hit it.”
Think about ways MC can torture him when they meet, how sweeeeeet
Lovers to enemies is a very underrated dynamic, you see. I’m just my contributing to the trope Leon
To be honest I don’t know how majority of people perceive her, but given her behavior as I mentioned earlier, I thought that might be a possibility.
I’m still not bored of RO’s that betrayed/betray you. If they seek forgiveness, there’s something cathartic about not being sure if you are willing to forgive them, the pain of being betrayed by a loved one and the possibility of the romance ending in blood 
Even though I get why people would hate M (sometimes my mc wants to punch them too), but she is still my favorite ro in wayhaven. None of the ros in wayhaven caught my interest except for Morgan, her hot and cold nature pulls me deeper and her rare display of affection for the mc just makes the scenes more sweet.
Idk if she necessarily hated (though i woukd get it lol),but i found myself trying to romance Maria from the relics series. I ended up failing though lol,so it didnt go far but i like the little insight into her softer side during your brief team up.
Oh, Maria is definitely hated. Pop over to my thread sometime and do a ctrl+f for “Maria,” you’ll see real quick. XD