Kururu

Kururu is the head of communications in the Keroro Platoon. Although he is of a higher rank than Keroro, he is not the leader of the Platoon due to his unpleasant and unnerving demeanor, which has given him the nickname of 'Yellow Devil'.

Kururu, a Sergeant Major in the Keron Army and the head of communications, is the brain of the Keroro Platoon. He is mischievous, deceitful, downright evil, and enigmatic, almost to the point where some people might call him a mad scientist. He is generally disliked by everyone, most of the characters seeing him as a depressing jerk and in the series, action figures of him tend to sell very poorly on Keron, (much to Kururu's chagrin but Kururu seems to take pride in his bad attitude). Despite this, he gets along quite well with Mutsumi and Aki Hinata. Kururu and Giroro greatly loathe each other due to their vast differences (Brain vs. Brawn) and as a result, Kururu usually uses Giroro as a guinea pig for any invention that he creates.

Kururu in childhood used to be blue. Kururu has an affection for curry, causing him to turn yellow. By the third season, Kururu seems to have developed a sort of crush on Giroro, much to the corporal's horror, blushing whenever Giroro pays extra attention to him, and wasting no opportunity to woo Giroro by way of gift or twisted invention. Whether this affection is genuine, or merely a new way for him to torment Giroro remains a mystery. Being the least emotional of the Keroro Platoon, he is almost never seen being moved to tears or smiles by any events, though at the same time he rarely, if ever, panics when something goes wrong, likely due to the multiple dangers from his own inventions outweighing it.