Keroro Gunsou Movie 2: Shinkai no Princess de Arimasu!
English name: Sergeant Frog Movie 2
Genres: Action, Adventure, Comedy, Drama, Sci-Fi
Type: Movie, Episodes: 1
Aired: Mar 17, 2007
Studio: Sunrise
Source: Unknown
Rating: PG - Children
Synopsis:
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)