During the Repliforce War, Double was assigned to the Hunters' 17th Unit under X's command, serving as X's operator while he was in the field. However, Double had actually been ordered by Sigma to infiltrate the Hunters' ranks and report their activities to him. When X set off for the Final Weapon, Double recieved orders from Sigma to follow him and destroy him. He slaughtered X's subordinates and stowed away aboard a shuttle before facing X aboard the Final Weapon and revealing his true intentions and true form. Double proved to be a vicious and savage combatant, but was unable to defeat X and was destroyed himself.
PersonalityDouble truly lives up to his name, being a double-agent with two different forms and different personalities. In his first form, he displays a calm, easy-going attitude and is also rather clumsy. When he transforms into his battle form, he becomes a homicidal maniac that revels in violence and is prone to ranting and outbursts of insane laughter. During his confrontation with X, Double mentions how he regards the Hunters, Repliforce and even the Mavericks as idiots, implying that he may not be as loyal to Sigma as previously thought.
- Alternate Forms - Double has two different forms. The first of these forms is that of a stout, rotund Reploid with a yellow chassis and apparently lacking any weapons or combat capabilities. His second form is taller, slender and appears to be mostly made up of a purple gelatinous substance. His body makeup in this mode has also earned him the nickname "Jello Man".
- Wrist Blades - Double has an energy blade attached to each forearm which he uses to savagely tear foes apart. His favoured maneauver is the Kiba Flash, in which he he pounces on his foe from above and then lunges again after touching the ground.
- Energy Blasts - Double can fire disks of crackling energy at his opponents and can even unleash this energy in a massive wave that is difficult to avoid.
Double is vulnerable to the Double Cyclone which will tear off parts of his gelatinous body. However, any parts of his body that break off can move independently and attack.