during a vacation Natsumi is visited by two male and female aliens named Meru and Maru.After becoming the Deep Sea Princess, Natsumi gains feelings for Meru who is haunted by this traumatic past. Having grown accustomed to Natsumi's ltitle, the Keroro Plotoon Expect a calm vacation.However their vacation is cut short and turns into a flight for survival as an alien creature Fuyuki adops reveals itself to be the kingdom and now sends creatures of mass destruction to assassinate Natsumi,and who stands.