Aika is a smart and athletic high school girl. She is so competent that she successfully passes the salvagers license test, obtaining a C-class license. Yet, she is young and hotheaded, so much so that Gota still treats her as a child. Due to this personality, no one is willing to hire her for salvaging jobs.

Since she had taken the trouble to get her license, she decides to post an ad in her school to attract clients. She manages to get the attention of Erika, a daughter of a rich family and the leader of the treasure hunting club. She asks Aika to salvage something from the sea and Aika delightfully accepts the request.

However, upon seeing the state-of-the-art submarine loaded onto Erika's private cruiser and discovering their destination, Aika realizes the terrible nature of her assignment. This results in a clash with a group of high school girls in the southern islands.

Who is the mysterious girl named Karen? So begins Aika's newest challenge!