Kat is the daughter of Naoki Himura.
In 2016, Kat and her mother moved to a new house. As her mother attempted to re-decorate the walls, she accidentally scratched a Celtic Monster Trapping Sigil, causing a Soul Eater to break free from its bounds.
Kat began hearing footsteps, and noticed her room temperature had dropped. Naoki brushed it off as a nightmare, so Kat asked for a glass of water. She told her mother that she did not like the house, but nothing could be done about it.
Suddenly, after her had mother left, the lights went off and the door slammed shut on its own. Terrified, Kat hid under the bed, and saw a shadow of feet. She was then grabbed from behind and dragged off, screaming.
The incident left Kat in a coma. Sam and Dean Winchester, posed as FBI agents, came to investigate the cause. The brothers discovered it was a Soul Eater and formed a plan to destroy it. Dean allowed himself to get taken to the Soul Eater's nest, where he encountered Kat and numerous other withering souls. Dean promised the girl that he would find a way out, and after both he and Sam finished drawing the spell, Kat found her mother (who had also been taken) and they returned to their bodies.