Kogitsune

A "young" spirit who befriends Natsume in the seventh episode of the first season, after being rescued from other yokai, who bullies him due to his gentle and shy nature. Because of this, he takes a great liking to Natsume, who also rejects to have his name for the Book of Friends and instead tells him they are friends. Occasionally he heads off to visit him and due to his inexperience as a spirit needs a potion to turn into a human child for a while.

It is implied that his mother has passed as when Kogitsune talks to what is supposedly a grave he refers to it as mom.