Hio Akira

Four years before the collision with the Great Comet, the aquatic mankind of Siren, who was on the verge of extinction, made a desperate effort to launch 12 fortress-type space probes into various parts of the universe. However, on the way, seven ships went missing, and the remaining ships were unable to find an oceanic planet that could be colonized, and it seemed that the Sirens were doomed to perish. At that time, the 12th ship "Mammut" discovers a habitable planet ahead. It was the third planet in the solar system, "Earth". The time limit until extinction is one year. There is no longer any time to look for a new place to live. Mammut Commander Zeran decides to invade with planetary remodeling. Humanity on Earth suffered tremendous damage from the sudden invasion, but began to fight back. Meanwhile, Hugh, a member of the established submarine squadron, helps a woman named Miranju in the chaos of the city. However, Miranju was a siren warrior who came to inspect the earth. The two meet on the battlefield and fall in love with each other.

A huge immigrant ship "Antilia" from the earth flew to the water planet Siren, and started to invade the whole of Siren, starting with the undersea city-state "Amoroth". Amoroth's guard captain Spalt, whose king and lover were slaughtered, advocated a total resistance and encouraged his subordinates to fight back, but they were helpless and defeated, swearing revenge and leaving their homeland. …Thus, the battle between the earthlings and the aquatic humans of Siren over the planet Siren has begun.