How do you take a protagonist and turn them into a convincing antagonist? Arcane does an excellent job of setting up the sister relationship between Powder and Vi. From there the story pushes forward and sets a strain on the relationship that continues to break. The key to making it convincing is to use little breadcrumbs for moments in the past. Powder's inferiority in the group was built from Episode 1 as a sore point in the story. Mylo is continually pushing her down and Vi spends most her time encouraging Powder while also making up for all her shortcomings.

These tension points are strewn throughout the story and so it makes sense when Vi has to make the choice whether to take Powder along for a dangerous mission or not. There are half a dozen moments that the audience realizes later have been building to this point, and it makes sense for Vi to leave powder behind. It also makes sense when Powder has a mental breakdown, as from her point of view, all her insecurities have come to light. Vi has abandoned her because she's incapable and every insult and biting word from Milo and all her own failures have been proved real.

It sets up the critical moment for Powder's transformation as at the last moment she arrives ready to save the day, only to accidentally kill her two childhood friends, almost kill her father, and wound her sister. All she wanted was to help and Vi explodes at her, striking her and calling her Jinx to name it true all her failures. We can see how the transformation took place and can look back at how the story has built up to this point which allows it to be shocking but not surprising. It allows the story to take it's character into newer and darker places while remaining true to who they are.

Music by Simon Swerwer,
Cuggin's Cove,
Emergence,
Inith and Od Travel North