n 200X, two worlds collided.... "World Half and Half Phenomenon!" Two worlds got mixed due to a mysterious phenomenon called the "World Mixing Phenomenon". In the new world, there exists the devil king. Actually, the world is a battlefield of two groups, Bloody Vampire, which is led by the devil king, and Social Kingdom. There is a school which is also used as a laboratory or proving ground. One day, the Bloody Vampire suddenly attacks there.... A fierce battle of beautiful heroines in battle armor called the Tetraveil now starts....