Kayn's Personality - Or lack thereof.
Riot, I commend you for Kayn's kit and his looks, as both are fun, edgy, and fairly unique in the game.
However, he's extremely lacking in nearly every other creative aspect. His lore (that we know and can divulge) is entirely unoriginal, trite, and as shallow as a kiddy pool. He's Zed's student who wants to overcome Zed. Oh lawdy, this is such a novel, new concept, a dark student seeking to overcome their master and use dark shadow powers to control the world or more, and intends to do so with a vile weapon he's gone into contract with. This guy is pretty much every anime trope rolled into one character - except lacking any unique personality that those characters have. Even Yasuo has better lore than this guy, and that's pretty bad.
And then there's his voice over. His interactions with Rhaast are trivial at best, and eye-rollingly bad at the worst. He's got the most mundane, tryhard personality I've ever seen, and it doesn't have any endearing qualities. He's mediocre, boring, and a character we have seen ad nauseum. Rhaast has more personality than him, and the sassy bloodthirsty demon in itself is a common trope nowadays. Neither one of them is particularly strong in conveying anything deep about their character, and together they're marginally better, but not much. This, of course, collapses in on itself when they choose to go Shadow or Darkin, as they lose the other voice, and fall into complete boring mediocrity. I would highly recommend he go back to the drawing board and have his personality revisited. At current, Yorick and the Maiden make for a more compelling duality than Kayn and Rhaast.
Ionia has such rich lore that you have yet to tap into. You've given us quite a few characters from Ionia recently, and the past 2 (Xayah and Rakan) have vague reasons for existing, but at least their campy personalities makes up for it. We actually know very little of Ionia, except that it's Japan where animal people live and the humans use magic and yoga to become wise, and that it was attacked by Noxus years and years ago. The whole story you've hinted at around Ionia (Shen/Zed/Yasuo) is mildly compelling, but so far, there's been no unique aspect to it - Jhin was actually one of the most unique things to come from Ionia, and even then, the hints in his lore don't give us much of an idea of how things are there. I would prefer to see things move in a direction that has a unique League of Legends flavor to it - and start straying away hard from the stereotypes and tropes that you're starting to fill Ionia with. It really is becoming a land that's too much Japan and too much of what we've seen before in anime and other games. Where is our Ionia like The Shadow Isles or Piltover/Zaun? Where are the unique intrigues of the nation that has pieced itself back together after a war, and strives to balance it's light with it's dark? Where is the lore that expands on the trio of ninjas (Kennen, Akali, Shen) and their role as enforcers for Karma as she tries to balance the good against the darkness? Where is the lore that encompasses the wild cards Syndra, Yasuo, and Varus as they tangle with the unseen warring factions of the government and the Shadow Clan? Please, you guys have a lot you can build around without resorting to common, shallow anime personalities, so I implore you to go back to your roots and build what you have that's unique.
