Set in a fictional MMORPG called The World, the series follows twins Shugo and Rena. After winning a contest, Rena is given a pair of chibi avatars in the design of the legendary .hackers, Kite and Black Rose. After an odd occurrence, a mysterious AI named Aura gives Shugo the Twilight Bracelet, an item that both aids and hinders him. Rena and Shugo embark on an adventure to find Aura and unravel the mystery of the Twilight Bracelet. Along the way, Shugo and Rena befriend other players: Mireille the rare hunter, the fierce Ouka,[notes 1] and the peaceful Hotaru. One night, while waiting for an event to start, Shugo and friends encounter a strange girl named Zefie, who is lured to Shugo because she believes the bracelet smells like her mother, Aura. It is later realized that Zefie is a vagrant AI - an AI that acts independently outside of the parameters of the game. Zefie's presence upsets many, including the Cobalt Knights, a group of administrators that follow the rule "If you can't control it, delete it" to an extreme. Meanwhile, Balmung, another administrator in The World, encounters problems of his own. The suits, CC Corp's upper tier executives, are displeased with what little action Balmung has taken against Shugo and his illegal item, the Twilight Bracelet. Balmung's administrative duties are revoked and he is fired.