I'll probably never watch the show but I want to know it had to have been something to explain
Well in the 2nd season (I think) Vanya kind of fucks off from the family and has a lesbian relationship with a late-in-life lesbian single mom. That relationship is the best thing to happen to Vanya and the happiest the character ever is. When Vanya rejoins the family in the next season he tells the family that she helped him figure out who he truly was and why he'd been so internally confused for all those years and insisted his name is now Viktor. He asks if anybody has an issue with that and the family members just shake their head and say not at all.
Basically, nobody loses their shit over it and just accepts him because they love him as a sibling, Viktor's character also becomes noticeably less broody than Vanya was which helps reflect how significant the change was.
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