Amelia Wil Tesla Seyruun ( アメリア・ウィル・テスラ・セイルーン Ameria Wiru Tesura Seirūn) is a young miko and the princess of Seyruun with an unwavering, quixotic belief in justice. She joins Lina's group during the first TV series. Amelia longs to be a "hero of justice" and quixotically pursues her quest by following Lina and fighting (what appears to her as) villains. Amelia's naive tendency to believe whatever she is told sometimes leads her to mistake friend and foe. In the novels, Amelia is the same age as Lina, but in the anime and manga franchise, Amelia is a year younger than Lina and smaller (though very busty, much to Lina's annoyance). In all incarnations of the franchise, Amelia's manner is that of a little girl playing a crusader.

She initially comes across as a naive young girl who can't distinguish between the good guys from the bad guys without relying on cliched stereotypes (such as her belief that "all villains dress in black"). However, her perspective upon good and evil matures significantly as the series progresses. Although Lina is often annoyed with Amelia for her naiveté, her desire to learn the Dragon Slave, and her larger bust size, eventually Lina comes to accept her as a friend and treats her like a little sister.

Most of Amelia's lessons in justice and heroism came from her father Prince Philionel of Seyruun, the "ultimate pacifist," armed with a variety of oxymoronic but very effective attacks, whom Lina once mistook for a bandit king (TV series). It is rumored that Naga the White Serpent might be Amelia's long-lost older sister, the crown princess Gracia (this rumor was later confirmed by Hajime Kanzaka during an interview). This rumor is played to great comedic effect in Evolution-R , with the character "Nana" and several ironic statements made by both of them that allude to the relation. After the murder of her mother, Amelia has vowed never to use blades, though she once used the Sword of Light to channel the Ra-Tilt.

Amelia becomes close to everyone in the group, but it is clear that early on she starts to develop feelings for Zelgadis, even though their first meeting was not a very good one. They become quite close as they tend to be together during missions—enough that Amelia can tease him playing chess, or angrily beat him over his treatment of innocent forest animals and get away without so much as an angry glare.

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