About Kai'Sa
Plenty of people have already said that Kai'Sa is a bit sexualized. If you want to argue "uwu by that logic, all the men in lol are sexualized too", fine. It's okay to have attractive characters. In a cast as large as League of Legends that seeks wide appeal, there's bound to be pretty women. It's okay to have attractive women characters. Kai'Sa falls into this camp. Now, I wouldn't say her design is bad. Riot rarely makes bad designs. Kai'Sa has a unique silhouette in League, which is hard to pull off in a game with 140 characters and counting. That being said, the decision for her to have a pretty face and a V-neck was safe... safe and rather boring.
A lot of LOL's women are attractive; some exist with sexuality coded into their character (e.g., Evelynn). Some have reasons and some are pretty for the sake of being pretty. Both are fine. Sexuality exists whether one likes it or not, and if Riot was to cut themselves from it, they'd be missing a lot of character opportunity. The problem, sometimes, is that they lean on it too heavily and they miss out on some opportunity. Ask yourself: Does the appearance serve the character, or at least not detract from it?
Rek'Sai was a breath of fresh air because she's female but otherwise a conventional monster. Her appearance suits her character. She's a Voidborn and feral. Given the trend set by the other Voidborn, it makes sense that a Voidborn female wouldn't abide by human norms. Illaoi was a breath of fresh air because she defies the usual physique of girls in LOL; her size fits her larger-than-life personality. Are you staring to feel me?
Just look at male champions, who have a greater range of shapes, sizes, and monstrosity. Take Tahm Kench. He has a cool design, but isn't conventionally attractive. He's clearly and unmistakably inhuman. Tahm is a voracious demon with an insatiable appetite who, despite all of the red flags, people would still trust in their desperation. Would Tahm Kench be as memorable if Riot made him an otherwise attractive man? His monstrous appearance, in my opinion, actually serves his character. It punctuates how much of a sweet talker he is, how desperate his prey are, for someone to trust something so clearly inhuman. Would Bard come across as so strange and whimsical if he looked more like a human in clothes? Urgot remade himself, replacing and adding mechanical parts to himself until he became a six-legged, biomechanical juggernaut. Would it have been as cool if Urgot just walked around on two legs?
Which brings me to Kai'Sa. A core part of her character is her lament that people only see her as a monster even though she's still human. There's some good opportunity there. But as many people have already pointed out, she's conventionally attractive beneath the mask. Let me restate that attractiveness isn't bad in itself, but sometimes it can detract from the story you're trying to tell. Does her attractive appearance make sense? Many of LOL's women are part of society and have access to beautification; some people just like to look pretty. But Kai'Sa wouldn't have access to that, having been trapped in the Void. But she has eyeliner, her face is seemingly well taken care of, and whenever her mask comes off she also gets a V-neck. Why? For the sake of being pretty, really. A safe decision, but misses out on some opportunity that her background provides. More than most, she'd have reason to have scars and a rough face. Some present the idea that the void suit keeps her beautiful, but why would it care? It's a Void symbiote and likely wouldn't understand what constitutes "pretty" to a human. She mostly hangs out in the Void underworld and since it wouldn't help her survive, it probably wouldn't think to do that. If it makes her look pretty so she can deceive humans into trusting her, then that'd make some sense. But she doesn't kill humans (perhaps you can argue that the suit's trying to do that anyway and she just doesn't give into its impulses, but again, looking pretty to trick people into letting their guard down isn't the Void's modus operandi. Evelynn does that, Ahri does that, LeBlanc does that. The Void is much more about brute force). Perhaps people in-universe think that it's just a trick, but we know that it isn't. Therefore, it detracts from her woe that everyone thinks she's a monster through and through. She's conventionally attractive to us, and therefore that character trait is harder to believe. It actually undermines the story that Riot is trying to tell. There aren't many ugly or unattractive women in LOL, and Kai'Sa had the opportunity to fill that niche. She has reason more than most. But Riot did not take it. They could have made Kai'Sa more monstrous or at least unattractive and it would've served her character more than most. Instead, they played it safe. That's the greater tragedy to me, from a character design point. Would the story of Brienne of Tarth have been more compelling if instead of being homely, she was conventionally pretty? Probably the opposite, because it does not serve her character and story.
