Zoruru is a gray Keronian frog with a metallic left side, including an extendable blade for his left arm, which serves as his primary weapon. His right eye is artificial, and his entire left face is covered by a metal plate. For reasons yet unknown, he harbors a deep grudge against Dororo and is solely focused on exacting revenge. During his platoon's invasion of Pokopen (Earth), Zoruru destroyed Mutsumi and Koyuki in an attempt to provoke Dororo into appearing. However, Dororo later revived them using his ninja powers by stabbing their ship.
Zoruru finally encountered Dororo at the end of the battle between the Keroro and Garuru platoons, where he revealed that he had little interest in the Earth invasion itself; his true aim was to seek out Dororo for revenge. Sadly, Dororo could not recall who Zoruru was and struggled to remember his name, mistaking him for Girara, Dasasa, and Tosasa—assumed to be former classmates. This lack of recognition deeply disappointed Zoruru, especially since it came from someone known for being frequently ignored. As a result, he slowly faded away. When the Garuru Platoon departed, Zoruru was seen in a recurring position, known as Dororo's trauma switch.
Following this episode, there is a running gag where Zoruru is repeatedly forgotten in one form or another, such as being the only one left out without an introduction in the special chapter of volume 13. In the Tokyopop version of volume 10 of Keroro Gunso, the letter "R" was written backwards whenever Zoruru spoke. However, this detail was dropped in the following volume and his brief appearance in volume 13. Source - Wikipedia.
