The old town of Tokyo is buried under water following a terrible catastrophe which has occurred several years before. Aika and her young partner Rion work for an agency specializing in the recovery of old relics, but the owner has serious financial problems. This is why it was decided that Aika again take up her old activities as a special agent...
Aika has been entrusted with a mission of collecting information on a material called "Lagu", but its progress was stopped by Hagen and his sister Neena, which have other projects for Lagu. Held captive on their vessel, Aika and Rion do what they can to try to escape. But it seems that the capacities of Aika are ineffecient against the new weapon of Hagen.
Aika with the assistance of her friend Gusto, succeed in escaping from the ship, leaving behind Rion. Her last combat left her weakened and she is no longer any match to face Hagen and his crew. During this time, Rion and Maypia, a spy whom they met, try to escape, but the projects of Hagen have already started to be carried out...
The team of Aika finds themselves involved in space in the hope to carry a term to the intrigues of Hargen of which all the parts are in place to put at execution its terrible plan. But quickly Aika will be confronted with an adversary of size, Neena. which carries on it an object which confers to him capacities semblabes with those of its gilded long-line bra from now on inoperative. The combat is announced hard
Even after the disappearance of its leader, the Delmo organization continues its activities with its only objective: taking its revenge on Aika. A secret operation is assembled to cut it down during its stay with the hotel.
An operation disguised in the form of collecting information on board a ultra-sophisticated plane, is worked out by the Delmo organization in order to secretly study the aptitudes of Aika for combat to discover her weaknesses. The latter not suspecting the trap which awaits her, accepts the work which is proposed to her.
During her overtime at the office, Aika is suddenly attacked by an agent of Delmo which manages to escape afterwards. Little time after, the building in which Aika is in explodes. Rion and her friends attend a funeral for their friend. With the assistance of Maypia and Gusto, Rion decides to infiltrate the enemy base to avenge the death of Aika.
Aika Sumeragi, a high school age C-Class salvager, is hired by class president Eri Shinkai to pilot her salvaging vessel. After introducing Aika to the treasure hunting club, and revealing coordinates hidden in a marking on fellow classmate Karen Minamino's chest, they embark on an adventure to see where it leads.
After arriving at the coordinates, Eri decides the treasure hunting club needs a break and declares that they will have a beach party on a nearby island. They are not alone, however, and Aika has to fight her teacher to protect Karen.
In the final episode of the series, Aika, Eri, and Karen find an old airport at the bottom of the ocean. After exploring the still functional facility, they finally uncover the secret to Karen's past.
