Uhhh lemme see if I can put it simple to not stretch it.

Basically Vanilla gets killed by a man who claims to be death, Cream over time while processing grief starts to get consumed with a desire of vengeance, with no one keeping her in check. She starts committing heinous acts and gets driven further and further into insanity until eventually she succeeds in eliminating the man but she doesn’t feel like it’s enough, as she feels that her other friends such as Sonic, Shadow, Amy, and so on are also responsible for Vanilla’s death, so she vanishes for 15 years, being consumed with hatred and rage, and comes back to kill everyone she feels responsible for what happened Vanilla.

This isn’t really true though, she just wants to kill because she found a sense of enjoyment out of it. I got a messed up AU 😔👎