"Only one can ride the ark..." Taniuchi Yuuji was leading an ordinary high school life. One day, Shuuichi, the older brother of his childhood friend Kageyama Miho, ruptured his entire body after setting an astonishing time in a track meet. Yuuji is then attacked by monsters one after another, and he discovers that he is an X-Gene with the genes of an extinct animal. Only one X-Gene can survive... The battle to determine the strongest gene now begins!