i've never understood the concern of having the characters of a game exist as if they're completely human.
in my opinion it ruins the creative abilities of those who like to create head canon. as soon as something is explained completely then there's no room to argue and the only people that benefit from that are those who seek to brag about how right they were. That glory is only moments long and once it's written out in detail the only way to remove it is a complete revision of the character.
the characters in a game like league honestly don't need stories because their entire personalities have always been a combination of memes, pop culture, and online meta references. in other words it seems very odd to give a moody character this weird happy go lucky joke that has nothing to do with anything - (read as why didn't varus get the memo). It conflicts and feels forced when a character who is supposed to have this fleshed out background story and tons of relationships fails to comment accordingly in a match and instead comments on the unsuspecting banana.
Kindred (read "Lamb") is a perfect example of a champion that has an amazing background that is completely separate from the entirety of the rest of the game and because of that there's this weird disconnect when a champion is marked by her, but her story has never been brought into question. Only her champion design because of wolf not feeling like a true 2nd character.
Jarvan IV is an example of a champion that feels completely out of place. He's supposed to be the king of demacia with tons of people to look after and at the very least you'd think he's heard of his opponents or address them in combat? nope.
Then there's a champion like zoe that talks to a few of the champions, but the things she says makes absolutely zero sense. If she's supposed to have waged war on darkin then why doesn't she talk to them? How did she meet Ezreal and become infatuated with him? How does she know Sol? How come she doesn't know any of the other Targonians? It just feels bad.
i guess my point is that it's not needed for the game. To me an interesting character isn't one that has this long detailed backstory that is defined and showcased to the community. To me an interesting character is one that can exist in isolation and stand on its own.
For characters like morgana and kayle it makes sense. It's a massive part of their identity in the game. They're supposed to be opposites and twins which is a ironic, but makes for a good explanation of their classes and fulfills a niche in the game.
for characters like yasuo, riven, and taliyah, sivir and azir, renekton and nasus, kayn, varus, and aatrox... it just makes it all confusing...
and 
are listed as "related champions" on universe for ages now, but we still didn't get told how. My personal guess is that Twitch will function as the villain for the hero Zac, but nothing official for now.
share a past with each other. While we know that it is likely that Vi is Jinx sister (Project Pyke semi-confirmed that), we still don't know how Warwick fits into the picture, all we have are theories.