Lance Corporal Dororo, originally named Zeroro, is a Keronian and a member of the Keroro Platoon, serving as its assassin and covert operations specialist. He is the last member of the platoon to appear in the series, and his primary color is a medium blue, though he is depicted as black in the original manga. His appearance is distinctly ninja-like, featuring light grey headgear and a mouthpiece that covers the lower part of his face. His forehead and belly are marked with a four-pointed shuriken symbol, and he always carries a sheathed knife on his back. A pink afro is part of his design, though it is seen less frequently.

Before arriving on Earth, Dororo, then known as Lance Corporal Zeroro, graduated from the Keron Military Academy. He served in an elite assassin squad under Captain Jirara alongside a soldier named Zoruru before being assigned to Sergeant Keroro's platoon for the mission to conquer Pekopon, the Keronian name for Earth. Shortly after the crash landing on the planet, Zeroro became separated from his comrades. He was eventually caught in a bear trap and, believing he would die alone, was rescued by a young human ninja-in-training named Koyuki Azumaya. Touched by her kindness and moved by the beauty and peace of Earth, he abandoned his mission to invade. He adopted the way of the ninja, changing his name to Dororo, which is derived from the forest where he was saved.

Dororo is characterized by a kind and meek soul, in stark contrast to his deadly skills. He speaks in a very formal and archaic manner, often ending his sentences with de gozaru, and refers to himself with the humble and old-fashioned term sessha. As a pacifist, he refuses to participate in any invasion plans that could be harmful to people's feelings, the environment, or the well-being of Earth's inhabitants, having developed a deep affection for the planet's flora and fauna. He spends much of his free time training, reading, tending to his garden, or quietly observing the actions of his platoon mates.

Despite his loyalty and formidable abilities, Dororo is frequently forgotten or overlooked by the other members of the Keroro Platoon, a recurring source of pain for him. This neglect stems from similar incidents of abuse and being ignored during his childhood, many of which were instigated by Keroro. When reminded of these traumatic memories or when he is blatantly disregarded, a psychological trauma switch is activated, causing him to curl up in a corner and cry. His closest and most significant relationship is with Koyuki Azumaya, who is often the only person who consistently remembers, encourages, and supports him. In the anime, they live together in a small traditional house in the mountains. He also shares a deep, if often one-sided, history with Keroro and Giroro, having been a childhood friend to both; he still looks up to them despite their frequent forgetfulness and mistreatment.

Dororo's skills in stealth and speed-based attacks are unrivaled within the platoon. His ninja abilities include running and climbing on vertical surfaces, leaping great distances, short-range teleportation, using log substitution tricks to avoid attacks, and creating shadow-capable clones that can act independently for short periods. While refraining from lethal force due to his pacifist beliefs, he is an exceptionally powerful fighter who often resolves conflicts with his abilities when necessary, providing moments of genuine awe in the otherwise comedic series.