Decoe is one of two primary humanoid assistant robots serving Doctor Eggman in the anime Sonic X, the other being his constant companion Bocoe. Decoe is characterized by his tall, thin, and golden-colored metallic body, which stands in stark contrast to Bocoe's short, round, silver frame. His design is notably similar to older Eggman robot henchmen from previous series, such as Scratch from Adventures of Sonic the Hedgehog, and his name is derived from the Japanese word dekoboko, which means unevenness or roughness, reflecting his irregular and angular shape.

In terms of personality, Decoe is portrayed as absent-minded, clumsy, and not particularly intelligent, serving largely as a source of comic relief throughout the series. Despite his lack of sharpness, he often acts as the more thoughtful and brainy member of the duo, frequently reflecting on the pair's constant failures or making snide, sarcastic remarks about Eggman behind his back, quipping about everything from the doctor's rash decisions to his excessive weight. While generally affable, Decoe can become irritated, particularly by the antics of Bokkun, another small messenger robot in Eggman's service. Unlike many purely functional machines, Decoe demonstrates that he has genuine feelings; he has been seen crying and shows a distinct appreciation for certain leisurely activities, such as figure skating.

Decoe's primary role in the story is that of a personal assistant and co-pilot, almost never straying far from Eggman's side or his latest mobile fortress. He is frequently tasked with overseeing the progress of Eggman's schemes, operating large flying fortresses, and managing various other machines and defenses. He displays little aptitude for direct combat, but he is a proficient pilot and has demonstrated a degree of skill in hand-to-hand combat, such as when he and Bocoe worked together to disable an opponent like Black Narcissus. He also has several unique combination abilities with Bocoe. One such combination, the Bokkun Beacon, involves Bocoe sitting atop Decoe to project a spotlight from his eyes to summon Bokkun. Another, the Decoe Bocoe Bazooka Fire, merges them into a functional energy cannon, and the impractical Vulcan Merge involves Decoe stretching his body over Bocoe's hands to fire projectiles. Decoe and Bocoe share a mutual fantasy of performing a powerful combination called the Decoe-Bocoe Cross to become a mighty battle robot, though this remains merely a dream.

Decoe's relationship with Doctor Eggman is complex. As his creator, Eggman is the authority figure Decoe is programmed to serve, and there is an underlying fear of Eggman's aggressive and threatening treatment. Nevertheless, Decoe remains largely loyal, aiding in schemes for world domination and piloting the Egg Fort. His key relationship is with his partner Bocoe, with whom he works in perfect sync, operating machinery and combining their functions. Decoe has little personal animosity towards Sonic and his friends, as his allegiance is based on programming rather than malice.

Decoe undergoes a notable, though temporary, development during the series. At one point, after Chris Thorndyke saves his and Bocoe's lives, the two robots become disillusioned with Eggman's constant mistreatment and threats of disassembly. They temporarily join Sonic's side and become more mellow and happy while serving the kind-hearted Thorndyke family as robotic butlers. This character development, however, is largely reset in a later season, where Decoe reverts to his original goofy and loyal henchman persona.