At best, Naga the Serpent is an alluring, enthralling, and awe-inspiring character. At the least, she is comical and impossible to ingore. Undeniably beautiful, impressively powerful, and amazingly self-centered, she doubles as both Lina's rival and her partner in crime.
Their strange relationship is a testament to Naga's odd place in the Slayers universe. She appears only in Slayers Great, Slayers Gorgeous, Slayers Return, Slayers Perfect (The Motion Picture) and Slayers Special, a compilation of six complete episodes. She never meets any of the other cast members, except for Gourry. (In Slayers Royal, the second Slayers RPG)
Whatever opinion you may have of Naga the Serpent, I think it's hard to deny that The Slayers wouldn't be complete without her.