Student Number 1 The helpless and meek ghost of a former student, Sayo Aisaka has low self-esteem and is not skilled at being a ghost, tripping even though she doesn't have feet and being completely unable to scare people, more often frightening herself than others. She is invisible to almost everyone, and her presence goes mostly unnoticed though Takahata had her included in the class registry, with a note to Negi not to change her seating. Sayo has been friendless and lonely for around 60 years since her death, which made her very desperate for a friend, and later attempts to talk to the rest of the class during the preparations for the School Festival. (Source: Wikipedia)

Spoiler

The school dean once comments about a girl who died around the time Sayo did, as the girl who was his first love. It is assumed that he is referring to Sayo. Manga version: Sayo attempts to show herself to the class during the Mahora school festival in order to make a friend, but the class interprets her clumsy communications as the work of a poltergeist, and tries to exorcise her. After Negi and Asakura calms everyone down, they're able to accept Sayo as part of the class. Afterwords, Sayo can always be seen by Asakura's side, as a sort of side-kick, although only Asakura and those with magic are able to see her at first. She eventually receives a palm-sized magic straw doll from Evangeline that allows her to move around with a somewhat physical body as well as allowing her to leave the school grounds.