Mii, also known as Mii-kun, is the caretaker of Mii-kun's Mansion of Life.
Mii was actually born as a cat. During her life as a pet she got along well with her child master. One day, bullies attacked her master and she fought them off but sustained fatal injuries in the process. After her death, she found herself on an empty planet and decided to use the planet as a sanctuary for deceased animals.
Mii is a character in the Galaxy Express 999 series, which was created by Leiji Matsumoto, who is popular for the Captain Harlock franchise and its related series. She makes her first appearance in Episode #37 "Mii-kun's Mansion of Life". In the anime series, her design and creation are credited to Shingo Arakiand Shigeru Kogawa respectively.