The story takes place in the year 2301 and Mars became a planet which mankind has tranformed into a place where they can life. Now the planet is known as the planet “Aqua” because most of the planet is covered in water. One day a 15 year old girl Misunashi Akari comes to the planet Aqua to become a Undine. This is where the story begins and we get to see what strange, funny, sad and mysterious events she meets.