Sgt. Frog, known in Japan as Keroro Gunso (ケロロ軍曹, Keroro Gunsō, lit. "Sergeant Keroro"), is a manga series by Mine Yoshizaki, launched April 1999 in Monthly Shōnen Ace. The series was later adapted into an anime television 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 platoon has many failed attempts at taking over Earth.
The series takes its comedy from a combination of wordplay (particularly puns and homophones), physical humor, situational irony, breaking of the fourth wall, and numerous pop culture references (especially to Gundam, Kamen Rider, Super Sentai, Space Battleship Yamato, Dragon Ball, Neon Genesis Evangelion and many others, although when broadcast and published in the United States, they make references that American audiences would be familiar with like Ghostbusters and Men in Black). 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 its animation studio, Sunrise, is a subsidiary of Bandai who does hold the rights to the Gundam franchise.
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