Four years ago, a mysterious mineral known as "Vuela" was discovered near the North Pole. Rumored to contain unique components not found anywhere on Earth, it was said to have miraculous effects in curing various incurable diseases. My father, Satoru Nagamine, invested a vast fortune to obtain its usage rights—his goal being the treatment of our twin younger sister Sayu, who had suffered from a congenital illness since birth. However, one summer day, Vuela suddenly vanished along with Professor Mochizuki, the lead developer. In the aftermath of this incident, an unknown heroine named ZERO appeared. Her motivation was not simple love or the salvation of humanity, but driven solely by one purpose: the determination to punish evil. As a result, she would ultimately face a BAD END.