Since the Kira clan and the Meigi clan were enemies, along with each respective clan keeping it's bloodline pure, a relationship between these two was forbidden. Kaya from the Kira clan and Kaltz from the Meigi clan in spite of that had a relationship. They kept their relationship a secret from their respective clan for a long while, but were exposed and naturally they were pursued. They ran from place to place in the forest, but Kaltz had gotten separated from Kaya along the way. It is later found out that Kaltz was trying to lead away all the pursuers away from Kaya.
However, some still followed Kaya and cornered her to which she ended up falling from the cliff of the Yuukoku Valley. She was pregnant with Asato during the time of the fall. Since she was close to Kira she was able to survive and give birth to Asato without any incidents. However, she was horribly weakened from giving birth.
Since Asato was not born in the form of a cat the people in Kira wanted to kill him, but Kagari the only other female in Kira intervened. Kagari started raising Asato along with Kaya, but Kaya passed away when Asato was still very young.
The only memento Kaya had of Kaltz was a flower petal that never withered. When she passed away that flower petal had turned into the only memento he had of his mother.