#what could've been...

[Note: These are thoughts I developed before s2 aired but I did know that Vi was most likely going to become an enforcer, and I will be addressing this question in regards to what season 1 set up, (not the motivations that we must haphazardly guess at based on what the writers of season 2 gave us). I want to get these thoughts down on paper in preparation for my own rewrite of s2.]

Let's explore some possible answers:

The reason can't be that she is upset over the actual act of launching a rocket on the council. She doesn't like the council or Piltover, to put it mildly.

Is it just the wanton destruction that bothers her? Vi has already seen this behavior from Jinx, and while each time it pushes her farther down the path of "my sister is gone," since this attack is, again, against Piltover, it falls a little flat that THIS one would be the last straw, even though it's the biggest in scale.

Could it all be for Caitlyn because of the the death of her mother? I think this could be part of her motivation, however while Caitlyn has made an impact on her for the short time they've known each other it's still been only a VERY short time. Not enough for her to go back on her lifelong dedication to her sister. (Yet this appears to be the only consistent explanation for Vi's actions in season 2 which just doesn't work based on what season 1 set up).

I believe there is a deep personal reason for this scene to break Vi's dedication to Powder. Vi's last interaction with Powder was to hurt her physically and even worse to confirm all Powder's worst fears about herself (when before she was always the one to keep these fears at bay). Vi became a monster to her little sister. This is indirectly explained in the scene where she tells Caitlyn about their childhood monster game (the "real monster" could apply to four different people in the scene).

Next, Vi is taken to prison. She states that the only thing that kept her going was the idea that she could get out and find Powder again, presumably to make everything right again, to live up to Vander's dying request, to reverse the moment where she became her little sister's worst nightmare.

However, prison ends up being the place where she descends into the monster again and again. The show addresses the fact that she is regularly beaten by the guards but barely touches on what is found in Vi's prison log in the Council Archives minigame, that she regularly fights with and beats her fellow prisoners in some cases beating them nearly to death. It's definitely possible that some of these people deserved it but at the same time it points to a troubling pattern of Vi allowing herself to sink to these extremes, drowning her pain in violence.

"If only I can get back to Powder I can make things right. This monster that takes over sometimes, it isn't really ME. I have a good heart, I'll prove it once I'm out of here, once I find her."

Violet's quest to save her sister is as much about her own sense of self-worth as it is about Powder.

That's the key to the final sequence. That's why the tea party, followed by the rocket attack, was what broke their sisterhood. After everything Vi tried to do for her, JINX rejects VI. Jinx can see the truth, that they can never go back, and snatches away Vi's shot at redemption and the foundation of her self-worth. Just as the old Vi whom Powder used to rely on is forever changed, the innocent little girl that Vi relied on to still need her is gone. Vi needed Powder to save her from her own inner monster. And Jinx walked away. In many ways these final moments are a parallel to Vi's "Because you're a jinx" to Powder years before.