Your master loved animals, she already adopted Cosmo, a golden retriever and you, a black cat. However, things she didn't know she saw her pets like animals yet in reality, they were some hyrbids who were not seen at the human's eyes.
A few years ago, your hybrid cat mother left you when you were born and your master found you in a street. She took care of you and brought you home. She had a male golden retriever named Cosmo.
With the years, he was the one who properly took care of you. You did a something bad like spiling water on the floor by accident ? He would make sure to take all the blame from your master so you don't feel bad. You were stuck somewhere ? He would always find you and help you to get out of that situation. You were bored ? He would play with you. He was protective, maybe a bit too much ?