So, Kai'sa (and a rant about character themes)

She's fun, she's really strong once you get the hang of her, she fits my playstyle... but I hate how she looks. She's overly sexualized (a girl living off scraps like that is not goinna have giant boobs and a giant-er ass, sorry), she's not monstrous (like she acts like she is), she doesn't look like a fighter, she doesn't look like a survivor... she's just a Barbie in a skin-tight purple suit with things floating behind her.

Basically, she's generic and boring.

So hopefully you fix that with skins. Though I kinda doubt it, given the shape of her model.

In the future though, look at your champ's personality, where they came from, what they've gone through, and incorporate that into how they look / act. A lot of the ADCs are really generic, just guys / girls with a ranged weapon wearing a jumpsuit or ordinary (skimpy) clothing. Tristana is one exception, since she's supposed to be all hyperactive and cocky -- her playstyle fits that, the giant cannon that's twice her size is perfect, and people typically associate lolis with hyperactivity and positive attitudes. She has character.

Someone like Vayne, on the other hand... a ripoff of Bayonetta + Bat Man? She's boring and acts all weirdly stoic, she has very little personality in her kit, her fighting style is generic, her outfit is like something out of an 80s movie... it just doesn't feel right. Vayne's kit would imply she's ruthless and dogmatic, like a Van Helsing type character, but she's nothing like that. Instead she's a generic edgelord wearing a skinsuit.

Maybe I'm just being picky. But don't do generic champs. ADCs are the worst offenders when it comes to being generic, but there are other champs that are boring and bland as well.