Dororo, formerly known as Zeroro before he went native, is a character in Sgt. Frog (also known as Keroro Gunso). He is the latest of the platoon to appear.
His body is medium blue (although painted completely black in the manga) with light gray ninja-like headgear and mouthpiece. His forehead and belly mark is a four-pointed shuriken and he always carries a sheathed knife on the back. His pink afro is the one seen more rarely. He is the last member of the platoon to appear, making his debut in the 7th volume of the manga, chapter 55, and the 13th episode of the anime.
As Dororo, he is a kind and meek soul, but his skills in stealth and speed-based attacks are unrivaled. He spends most of his time training, reading, or spying on the actions of KeroroPlatoon and others. Dororo is often forgotten by the rest of Keroro Platoon, causing his psychological trauma switch (something created from similar childhood incidents of comic abuse and neglect, most of them Keroro's fault) to turn on, making him sit in a corner and cry. Also, Dororo will not participate in plans that are potentially harmful to people's feelings or well being, the nature, etc.
Dororo speaks very formally and often ends his sentences with "de gozaru", an archaic form of 'desu'. His laughter thrives from the word zaru. Dororo's self referring nickname, 'sessha', is an archaic male form of "I", primarily used by samurai. He has a small crush on Koyuki, but it is not easily shown.
Then known as Lance Corporal Zeroro (ゼロロ兵長Zeroro Heichō), he graduated from the Keron Military Academy under the rank of Lance Corporal. After serving alongside Zoruru in an elite assassin squad, under the command of Captain Jirara, he was assigned as the assassin of the Keroro Platoon alongside Keroro, Giroro, Tamama and Kululu. They were given the mission to conquer Pekopon. After crash landing on Pekopon, Zeroro was rescued by ninja-in-training Koyuki Azumaya (in the anime, he was rescued by Koyuki and her dog Zeroyasha). Wishing to follow the way of the ninja, Zeroro changed his name to Dororo.
His reunion with the rest of the platoon does not start well, since he just appears to resign because he no longer shares their invasion objectives. However, after he and Koyuki are captured by Viper and the platoon comes to rescue them, they mend their friendship and he rejoins the platoon, after making them steam a bit. In the manga, he and Koyuki move to a house besides the Hinatas, but in the anime they live in a small traditional house in the mountain, bordering the Nishizawa state.