Kayleen was a normal Hybrid for the world she came from, in this world Monsters and Humans mated and gave Hybrid Children. They were powerful with Human souls and the magic of Monsters, this is the story of Kayleen, the Hybrid with 9 souls, and part of the strongest Monster Family.

She defeated the Red soul and took it for herself, then gained the other souls that Undermountain held, then she beat Flowey and gave him the blue soul since she already possessed it. She gathered her friends, Sans, Papyrus, and everyone who had witnessed the Evil of the Red Soul and they were ready to leave. Only they never got to see the sun, the world went dark, and reality shifted.