What stands out to me here is that it seems like Yone was designed in a very "top-down" way. Rather than starting with an idea for a kit and creating a concept, they began with the idea of Yone and designed a kit for him. Both his fleshed-out backstory and his kit evolved from a desire to make Yone a champion.
I don't remember whether that was the case for Senna and Kai'Sa as well, but either way, it's cool to see. Most League champions seem to be designed "bottom-up", so seeing some top-down design like this is really interesting to me. I think it paid off, because his kit seems really effective at reflecting his story and lore.
This whole article is actually a really fascinating look into how narrative and gameplay design intersect in League, with a lot of moments of one influencing the other and vice versa. It's a great read for that reason.
It was for Senna, but I am unsure about Kai'Sa (I wasn't at Riot then). EndlessPillows mentioned that he loves designing champions that are already someone, and using their story as a huge influence. The Yone team is incredible. They put so much passion into him. It was so clearly palpable from the way they talked about him.