You go up to the safe and pull out a book. It's the manuscript written by your grandfather, presumably shortly before you suspect he died. It's titled Samus Libri. You think that's latin for live free, or something. In reality it just means Sam's book. Sam, the author and your grandfather, seems to be a human, based on his name not being anywhere close to cat-related.
Upon further observation, the last name, Severon, seems an awful lot like Suki's. Yes, her last name was Severon. Suki Severon. It must be a relative. But that must mean that you and she are related, if only cousins of variable distance. Now, why your last name isn't Severon also is a question of cat society. In Cat society, last names aren't inherited by paternal connection, no, it's inherited by whoever's older. Your grandmother was older than your grandfather when they were in love, so your father inherited her last name. Now, your mother changed her last name to your father's when they married a few years before you were born, so you had no question of "which last name is the real last name", it was just meowrosa.
You feel the need to list the last names of your friends. Mew Mew's last name is technically "Mapstablook". Their father's last name was Bapstablook, so I suppose it's just imposed onto the children of the blooks. Syb's last name is a little unclear. When you first met, he had no last name. Just "Syb". But one day, his sister was trying to get a driver's license because she was old enough to, and she needed a last name to legally do the test. She was learning Japanese at the time, so she gave the Japanese word for bird, Tori, as their last name. She didn't pass the test, but without Syb's knowledge, he gained the last name Tori. Then there's Suki's, Severon; and you, meowrosa.