Jin Kanzaki is poor, but he lives a happy life with his grandfather. Together with his friends Kouga and Konoha, he helps people for a fee. Meanwhile, the police are searching for a vicious serial killer.

A few years have passed since Jin went missing. Kouga, still dreaming of becoming a real hero, is intent on catching a serial arsonist prowling the streets.

When Jin wakes up, he sees a monster holding the lifeless body of his foster mother, Akemi. An old man named Mitsugai is attempting to awaken ZET within Jin by using her. Mitsugai succeeds and ZET awakens, but he's still incomplete.

Two years have passed. Players are wreaking havoc in society, but humans are still unaware of their existence. People live in fear, and Mitsugai is unable to produce another ZET.

Kouga tries to become a superhero by creating a real-life Alphas. A mysterious man approaches him with a test to see if he's qualified to become one. Kouga must now choose between the life of his sister or three strangers he has never met.

Konoha is taken hostage and Jin is unable to do anything. Unlike before, he cannot become ZET by hurting himself and doesn't have his Activation Gum.