Naga's real full name is Gracia Ul Naga Saillune, making her the first daughter of Crown Prince Philionel El Di Saillune and the older sister of Amelia Wil Tesla Saillune.

Although, Naga is the older sister of Amelia Wil Tesla Saillune, the pair have never met in the series when both were aware of the other's identity.

Naga's mother was murdered before her own eyes several years before the start of the series by the famous assassin Booley. As a result, Naga slayed her mother's killer with the crown princess' original spell, Chaos String. After the funeral, Naga found the outrageous outfit she currently wears inside her mother's closet. Shortly afterward, she left home in order to learn the ways of the world.

Being a princess, Naga knows when to be graceful, and when to be self-confident. Although she keeps her true identity secret, she acts in a self-confident and sometimes arrogant manner.

The only Slayers' character Naga really interacts with is Lina. Naga the Serpent is Lina's rival and companion through the first four movies and both OVAs. She acts as a constant annoyance for Lina due to the fact that she is more, she is a very powerful sorceress, but faints at the sight of blood and is quite clumsy. Throughout their adventures, Naga and Lina often end up on opposing sides and have to fight, but they always end up traveling together again. Nevertheless, the pair will often work together despite their differences, and when they do, they are a great team.