Spoilery explanation from my understanding of the event's story for this Roza who happens to be an AU version of Roza where she got very badly injured trying to help an injured Lili escape. Liliya choose to undergone a procedure to save her sister but at a cost of herself, Liliya is still alive but she is now fused into Roza, her conciousness resides in Roza's tail now
as Delta, Roza is edgier and isn't cheerful anymore. She still has some semblance of her old self popping up here and there, she also dislike being refered to by her original name.
Extra note: unlike regular Roza, you can't display Delta with Lili on the homescreen
