"Slayers Premium" is a one-volume manga that serves as a side story within the larger "Slayers" universe, written by Hajime Kanzaka and illustrated by Rui Araizumi. The narrative centers on Lina Inverse, a powerful sorceress known for her fiery temper and immense magical abilities, and her companion Gourry Gabriev, a skilled swordsman with a laid-back demeanor. The story unfolds in a fantasy world filled with magic, demons, and adventure.

The plot begins with Lina and Gourry encountering a mysterious girl named Milina, who claims to be Lina’s younger sister. Milina’s sudden appearance raises suspicions, as Lina has no recollection of having a sister. The duo soon discovers that Milina is being pursued by a group of powerful demons, who are after a magical artifact she possesses. This artifact, known as the "Premium Orb," is said to grant immense power to its wielder, making it a target for those seeking to dominate the world.

As Lina and Gourry investigate Milina’s origins and the true nature of the Premium Orb, they are drawn into a series of battles with the demonic forces. Along the way, they encounter familiar allies, including Zelgadis Greywords, a chimera swordsman with a tragic past, and Amelia Wil Tesla Seyruun, a justice-loving princess and sorceress. Together, they must unravel the mystery behind Milina’s identity and prevent the Premium Orb from falling into the wrong hands.

The story explores themes of trust, identity, and the consequences of wielding power, as Lina grapples with her doubts about Milina’s true intentions. The narrative maintains a balance of action, humor, and character-driven moments, staying true to the tone of the "Slayers" series. The climax involves a high-stakes confrontation with the demons, revealing the true purpose of the Premium Orb and its connection to Milina. The resolution ties up the central conflict while leaving room for the characters to continue their adventures in the broader "Slayers" universe.