This papercraft is designed by ronin. Sgt. Frog, known in Japan as Keroro Gunso, is a manga series by Mine Yoshizaki. It was later serialized into a TV anime series directed by Junichi Sato. Both the anime and manga are comedies that follow the attempts of a platoon of frog-like alien invaders to conquer Earth. Sergeant Keroro, the titular character, is the leader of the platoon, but is at the mercy of a human family of three after he is captured while trying to hide in one of the family member's bedrooms. In both the manga and anime, Keroro is forced to do meaningless chores and errands for the family after his army abandons his platoon on Earth.
The series takes its comedy from a combination of wordplay, physical humor, situational irony, breaking of the fourth wall, and numerous pop culture references (especially to Gundam, Kamen Rider, Space Battleship Yamato, Dragon Ball, and Neon Genesis Evangelion and many others). Various anime, games, manga, and other aspects of pop culture are parodied/referenced throughout the series as a bonus to older viewers. Both the manga and the anime are laden with pop-culture references, and even in the same story the references often vary wildly. The anime does not explicitly refer to Evangelion or other animations to which Bandai does not hold the copyrights, but only recreates the "feel" of famous scenes from these anime. The anime is much more detailed and direct in its Gundam references, however, since Bandai does hold rights to the Gundam franchise.