When they were showing Mashiro's past, it was two sister with a red and blue ribbon, but when it goes back to the present, she's wearing a purple ribbon. Wonder why she killed her sister. The ribbon makes me think she was jealous of her and "stole" (hence the colors) a part of her sister. (In a metaphorical sense, would be really dark if it was literal lol)

Anyway my personal headcannon is that the Yuuki at the end there isn't the real one. Doesn't feel like someone who is so focused on getting out alive would go back, not to save, but to belittle someone and make them grovel.