Long ago, there was a mystical kingdom called Atlantis located to the west of the beautiful city of Eden. Generations of Angels lived and worked there in peace. However, this peace was soon overwhelmed by the ferocity of war. After the war, Atlantis was torn from the land and sunk beneath the waves. Even after this tragedy the people of Eden sought peace. Recently, scientists from the Iron Castle Exploration Association have found the exact location of Atlantis. The first cooperation among four factions in history was created. They have created a great exploration ship, Habosen, and planned to go to Atlantis. While Angels all over Eden cheered their bravery and hoped for the best, evil shadows gathered under the water.