When Gennai was trying to escape Piedmon and his troops with the soon to be Digidestined's Digimon, something happened that changed one of their lives. One of Piedmon's troops shot Gennai, as he moved to get away from it, one digiegg dropped into a nearby island. As a couple of years passed, the digiegg hatched into Nyaromon, she knew that she was waiting for someone but didn't know who. So as years passed, she waited and waited, but no one came, so then she digivolved into Salamon and started searching. One day, she found someone but not the person she was looking for, it was evil, Myotismon.
So the days of torture started to begin, every time she disobeyed him, he had to punish her by using his whip, every time she looked at him with those eyes he hate, he did it again. Now after these punishments, she became a faithful servant and digivolved into Gatomon. She did everything he commanded and much more.
When Myotismon found out about the eighth child, he and his slaves went in search of him(her) in the real world. Gatomon was mostly incharge of finding him, so Myotismon had made copies of his crest so when he was near, it would still light up. So days passed, but still no luck until one day in the park/forest, Kari was running after Miiko while Gatomon was in the other direction. Kari knew that Gatomon was not an ordinary cat but one of them, the Digimon. So Gatomon thought that she could be the eighth child and followed her home.
On the way to the Kamiya's apartment, Gatomon was right behind her, Kari already knew she was following her, so she let the door to her apartment open. Gatomon tried to attack her but she couldn't because every time she was near her, she had this feeling. So she kept trying and trying to attack her but the same feeling stopped her.
So then Wizardmon helped her to remember her past, she remembered all the torture of Myotismon and that one day, she helped Wizardmon to live and she told him her mission of finding someone that she belonged with. So then Wizardmon gave her the digivice and went to Kari and then the digivice lit up and Gatomon knew that she was waiting for her, the eighth child, Kari.