Words Fly Away, Those Written Remain

is the 19th episode of the Negima!: Magister Negi Magi (anime).

Summary
Kazumi starts investigating about a "ghost" classmate who happens to be the academy's earthbound spirit for many years.

Differences from the Manga

 * In the manga, Sayo's official introduction takes place at the start of Mahora Festival and features her trying to make a presence to the class, but is mistaken for a vengeful spirit and is almost exorcized by Setsuna and Mana, but is saved in time by Negi and Kazumi who're investigating about her origins. With the misunderstanding cleared, Sayo successfully becomes friends with the class.
 * The anime reveals Sayo's past and her family members while she was still alive and her being possibly being romantically involved with Konoemon Konoe. As of the end of manga, Sayo's past is only partially hinted in story in her Cosmo Entelecheia with her dream consisting of her with an unknown man, commonly believed by fans to be the young Konoemon. This would later be confirmed in Chapter 183 UQ Holder, where it is revealed that Sayo was in love with him while she was still alive as a human.
 * Because of her remembering about her past at the end of this episode, Sayo is no longer confined as an earthbound spirit at Mahora Academy and can now leave at will, allowing her to join the class on the trip to Tokyo.

Trivia

 * Thought not stated and only implied onscreen, the cause of Sayo's death in this adaptation appears to be Pneumonia.