Holy fuck Riot. I comment the balls you have in changing Varus's backstory.
Personally I don't care about someone's sexual orientation because 999/1000 times people is just force onto the masses because they want too look good and fear losing their "good guy" badge, which is a shitty way of trying to prove you are a fundamentally good person.
But enough about my rant and here is why I am not holding a pitchfork and a touch in my hands. Varus's backstory was "hollow" and common. Sure he had the motivation of avenging his family and all, but it just didn't add any flavor or bring out anything unique about him as a character. the thing is that Varus was a like a blank slate in spite of having a backstory, which made Varus a long over due candidate for a lore rework.
What was amazing about Varus's new backstory is just how two people got bonded and fused together with each other and the Darkin to become the current version of Varus. That is the aspect I like the most about his lore now.
That other part is that you have connected a lot of things about the Darkin and explain it to us through the backstory. The fact that Valmar and Kai are still able to resist Varus and that they are a good foil to Kayn. One pair that is in an uneasy alliance that who's battle for dominance will come swift and sudden, while the other is a gestalt of two lovers that are fighting to a slow and uncertain conclusion.
What is also a thing I like this that we get too see Val and Kai as people, not a forced token gay couple, and that makes the story more unique. It also make show the love that Varus The Darkin has for his kin. So there is a "light love" of Val and Kai. And a "dark love" that Varus has for his kin, with him looking for his sister at the end of his short story.
10/10 Riot. Respect to you being so bold.