Amelia Wil Tesla Saillune, also known as Amelia Wil Tesla Seyruun, is the second princess of the kingdom of Saillune, a realm renowned for its mastery of white magic. As the youngest daughter of Crown Prince Philionel, Amelia is a youthful and energetic sorceress who is deeply committed to her self-appointed role as a champion of justice. She is typically portrayed as being around fourteen to sixteen years of age, with a short stature that often becomes a point of humorous comparison to her more developed figure, much to the chagrin of her taller but less endowed companion, Lina Inverse.

Amelia's personality is defined by her unwavering, and at times extreme, idealism. She views the world in stark terms of good versus evil, a perspective she inherited from her father. This manifests in a habit of delivering passionate, rousing speeches about truth and justice, often from the highest available vantage point, a practice that just as often ends with her clumsily falling to the ground. Despite her noble birth, she is not haughty; she is kind-hearted, compassionate, and unfailingly polite, usually addressing even close friends with formal titles like Miss or Mr.. However, her naive and scatterbrained nature can lead her to misjudge situations, sometimes causing more trouble than she resolves. Her obsession with justice serves as a coping mechanism for a traumatic childhood, which included the murder of her mother when she was very young and the subsequent disappearance of her older sister, Gracia.

Amelia's primary motivation is to spread justice and protect the innocent, a goal that drives her to seek out evil and right wrongs. She joins the protagonist Lina Inverse on her journeys not only out of a sense of adventure but also to clear Lina's name and to learn from her, viewing the powerful sorceress as a hero to emulate. Her role in the story is that of a steadfast ally, providing moral support, healing, and formidable magical offense. As the series progresses, she grows from a somewhat oblivious tag-along into a more competent and confident individual, taking on leadership roles, such as commanding a battalion of mages from her kingdom.

Amelia's key relationships deeply influence her development. Her friendship with Lina Inverse is central; initially, she idolizes Lina, but this evolves into a genuine sisterly bond where they support and bicker with each other as equals. Her relationship with the chimera Zelgadis Greywords is a significant subplot. Though she finds his appearance frightening at first, she comes to see his good heart, and the anime series strongly hints at a growing romantic affection between them, with Amelia often being the one to keep his cynical nature in check. She shares a respectful and supportive friendship with the golden dragon Filia, while her interactions with the mysterious priest Xellos often involve her overwhelming him with positive affirmations about life, which he finds uncomfortable.

In terms of abilities, Amelia is a highly skilled magic user with a focus on white magic, reflecting her status as a princess of Saillune. She is also proficient in shamanistic magic and has even been known to cast powerful black magic spells on occasion. One of her signature spells is the Ra Tilt, a potent shamanistic invocation she refers to as her killer spell. Unlike Lina, who relies on ranged attacks, Amelia prefers hand-to-hand combat, often channeling magic into her fists. She developed a unique spell called Visfarank, which creates magical boxing gloves of energy to pummel her foes, allowing her to strike creatures that are immune to physical blows. Despite her magical prowess and surprising physical durability, she is not particularly agile and can be a clumsy target in a direct fight.