I seem to recall Patchouli calling Remilia an old friend, but beyond that who knows what their relationship is or what's going to happen. I kind of expect critical unfinished business, considering how fast she dropped everything to go chase down Remilia.

Could she have been involved in the attack on Scarlet House?

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Authors of our fates
Orchestrate our fall from grace
Poorest players on the stage
Our defiance drives us straight to the edge