a thought came to mind regarding each champion's relationship with other characters...
After watching the video on Nunu and Willump's special interactions with other people, I've noticed that this is something Riot seems to be doing more with most of the champions; giving them some sort of special relations with other champions so that the whole world seems more connected. While I'm sure we'll be seeing this more in not only future champions, but future VGUs as well there's one champion who never really got that ability to connect with other champions despite being in a way, one of the "Villains" of the league universe: Karthus.
Maybe it was because Karthus's VU was done before Riot decided to make champions more connected with each other, but it does give a feeling that despite Karthus's rep in the Shadow isles, his position is sort of a solitary one. Any other champion lines (taunts/responses) are simply either acknowledging he's from the Shadow Isles, or his title as Deathsinger. I was surprised that Swain never gave Karthus a line considering both of their motifs are death-related, and you don't really hear any special taunt lines for him outside of a couple other Shadow Isles champs or Kindred. It certainly doesn't help that if you look at any official Riot stories involving him, he never really has any connection to anyone outside of the Pentakill universe.
Thankfully, it's not too late for this to change. As I understand it, Riot intends on giving a Bio update to Soraka soon, someone who has always been stated as a "Rival" of Karthus in the history of league (mostly because of thematics). If I may suggest, can we add some sort of story giving the 2 something for the 2 to be rivals besides simple thematics? (please, nothing like "Oh his motif is the exact opposite of mine, we should fight!") I'm just saying, it would be nice to give Karthus some additional story that actually connects him to the rest of the Universe