I think Kayn is cool
I like Kayn because he is pretty interesting and there's a lot of questions surrounding him.
Rhaast and Kayn meeting Before? As a child we know nothing about Kayn except he was something Noxus could just pick up and put into their armies. Meaning he could be an orphan or could be whatever but we know that he most likely wasn't that high up in Noxus.
When sent to the battle he for whatever reason fought and with a ton of effort. We have absolutely zero idea as to why he fought with insane conviction but he did. Honestly I'm thinking that Kayn in youth somehow made contact with Rhaast and that's why he fought so much and why he didn't care for using weapons except his own body. Looking at Kayn's voice lines he shows hostility towards Noxians, "Your kind go no further", and he also taunts them when he kills them and stuff. Why would Kayn fight so hard against the Ionians? He also had the chance to run away like a few other kids but instead he fought and met up with the Noxian soldier flank. This hints more towards something in Kayn (meeting with Rhaast) that pushed him towards fighting.
But as he felt Noxian soil beneath him for the first time in years, amid the enemy soldiers slain and soon to be forgotten, there was unease. It hung in the air like the pressure before a storm, begging to be released. (...) Kayn said nothing. His hands rested empty at his sides. He knew he was in control. Even so, he felt a flickering sense of déjà vu, like something out of a dream. It came in a flash, and then was gone.
I think these line in his short story kind of hints at that. I think the unease is because he was near Rhaast and he was like drawn to him kinda. Also that they met in the past somehow, that's the already seen.
A kinda friendly relationship? Right off the bat when locking in Kayn we get dialogue like this: Kayn: "Will you prove worthy?" Rhaast: "Probably not."
The two also are constantly talking to each other and it's not like "I'm gonna control you" all the time. But just a bunch of shenanigans. They also share a distaste in fighting the scuttlecrab. Rhaast shows a lot of admiration and enjoyment in Kayn's shadow abilities. Rhaast jokes when Kayn buys another weapon. There is a constant struggle of control between Kayn and Rhaast but it doesn't consume their entire lives. Also I'm getting insane Soul Eater vibes from Kayn and I can't help but imagine the two working together to take down difficult enemies.
Weird Kayn Stuff Kayn is kinda weird because he is arrogant but that doesn't seem to screw him up. He is patient and also accurate with everything.
He shows a bit of remorse when going against Shen which is weird. We have no idea of his relations to Shen. One could guess that he appreciates Shen's spirit balance work but that makes no sense because one of Kayn's goals is to be boss of the Shadow Order. A better guess is that Shen has done well for Ionia and maybe that is why Kayn doesn't want to kill him. But that's assuming Kayn like's Ionia kinda... So this is kinda weird how he doesn't really wanna kill Shen.
We also get some more of his character if he kills Zed. Kayn is arrogant and wants to rule the Order of Shadow but he also likes Zed and isn't about killing him. He wants a proper paper work promotion it seems. This shows how Kayn isn't about killing everyone and stuff.
As a Shadow Assassin he has the line "Revenge" when attacking Sion which is weird. Maybe Sion was used in the Ionian Invasion?
He has lines like this, "The true assassin kills one to save many." but also has lines for when he gets a bunch of kills which is also weird. And also pretty violent lines like "Their screams will echo from this place". He also has some dialogue with Rhaast: Rhaast: "Oh how I miss the smell of blood in the water." Kayn: "Today you will be reminded."
He also has a Sun Tzu quote (kinda): "Wait by the river long enough and the enemy dead will float by." Which shows more of his patience.
I think Kayn is cool cause he has cool hair and is pretty interesting.