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Naga was often found hanging around Lina Inverse during Lina's earlier adventures, but the two had later parted company under unknown circumstances. During the time that they were together, whenever Naga was around, she was either working together with Lina or against her, all the while irritating the red-headed sorceress to no end.

Naga claims she is Lina's only serious rival. Lina calls her "goldfish feces" — as in, she trails after Lina. Like Lina, she has a massive appetite and is an excessive alcoholic. She is extremely well-endowed, much to Lina's disgust and jealousy, and wears very little clothing (it is characterized in the OVA as the "evil sorcerer look" and as an even less respectable sort of look).

It is hinted at throughout the different Slayers series that Naga is really the daughter of Prince Philionel El Di Seyruun, and the oldest sister to Amelia Wil Tesla Seyruun. While creator Hajime Kanzaka confirms this, it's a fact that has yet to surface within any of the series' major incarnations.

Naga appeared particularly in the OAV’s and movies, however there is a debatable cameo appearance by her in the first season of the TV series midway through (during a crowd scene, several people walked in from of the 'camera' including a shapely lower torso that bore an uncanny resemblance to Naga's design, though the long trailing hair was red so it may have been an homage, or potentially Serena from the second OVA series who became a follower of Naga's. Amelia notices the character during the brief scene.

Source: Wikipedia