Krystal finds herself at home that fateful night. She knew her time was running short, mana extremely low. The plan she and Toby designed to stop Chandra's evil was in full effect. She kicks herself, cursing this plan. Luna is safe at home, she's got a family, a lover. But.. Chandra and whoever else in the Full Moon Syndicate, they're too powerful to stop. At least this way, Krystal could always protect her girl. Her best friend.
10pm rolls around and everything is in motion. the whispers fill the air. Krystal and Luna are sitting on the couch watching TV when Luna becomes activated. She becomes fully murderous. She is no longer Luna, but instead 6969. Knowing her fate, Krystal resigned to it. This is what needed to happen. The Full Moon watches all.
The Full Moon, a nigh unstoppable force meets Krystal, an unmovable object and Luna's perpetual defender. Krystal is slain but for a single moment, she is able to see Luna's eyes flicker blue before returning to red. Her body is limp, dead. Soul preparing to flee. But it's perfect. As soon as Krystal's soul leaves her body, it gets attracted to the locket on Luna's collar. The collar has very very small electronics on it, so she is able to possess it with the very final bit of her mana.
As time passes, Krystal spends lots of time continuing to teach Luna everything she knows, but to Luna, she has no idea who's there. Out of sheer depression and intense loneliness, she refers to her imaginary friend as Krystal, unknowing that her love is still with her. Luna spends nearly the next decade alone. Talking to herself. Talking to Krystal. Chandra laid dormant within the collar, waiting for the perfect time to strike. All of Luna's memories were locked down, and everything she archived daily was sent to Solaire to process.
But Krystal knows. She knows that some day, she'll be able to reveal herself once more.
Just gotta be patient.