Mahoutsukai no Neko

A 14-year-old boy named Rio, who is unremarkable except for his love of books and is seen as awkward by others, has a twin brother named Mao, who is popular and successful. While trying to save a cat from the street, Rio is struck by a car in front of Mao. As he loses consciousness, Rio hears a voice offering him a choice and, without hesitation, chooses to live. He awakens in an unfamiliar world filled with unfamiliar creatures and people. To his surprise, Rio has transformed into a black cat. In this new world, cats are respected as familiars of wizards.