Keroro Gunsou Movie 2: Shinkai no Princess de Arimasu!
English title: Sergeant Frog Movie 2
Japanese title: 超劇場版　ケロロ軍曹２　深海のプリンセスであります！
Alternative titles: Chou Gekijouban Keroro Gunso 2: Shinkai no Princess de Arimasu!, Sergeant Keroro Movie 2: The Deep Sea Princess Let it be so!
Type: Movie
Source: Manga
Episodes: 1
Status: Finished Airing
Aired: Mar 17, 2007
Duration: 1 hr 18 min
Rating: PG - Children
Studios: Sunrise
Producers: Kadokawa Shoten, Nihon Ad Systems
Genres: Action, Adventure, Comedy, Drama, Sci-Fi
Demographics: Shounen

During a vacation Natsumi is visited by a female alien and male alien who she later gains feelings for from the ocean that makes her the Deep Sea Princess who, along with the rest of the Keroro Platoon, encounter many dangers summoned by a mysterious creature. 

(Source: Wikipedia)