Sometime in the future, Kei and Ai are running for their lives. Ai is a little girl, who holds a terrible secret which could destroy the world populated by Headmeters — people who have psychic powers and their strength is shown on their forehead when they fight. Kei on the other hand was an experimental subject and his strength never went above level 5 while others surpassed his ability effortlessly. However, in desperate moments, Kei can infinitely increase his ability when protecting Ai.

The leader of the pursuers, hounding Ai, has a dark secret and is aided by a small dwarf-like man in a robotic suit. When Ai is eventually captured, Kei, a detective and another Headmeter must rescue her and "save" the secret which she holds.

But what is this secret? And who is Ai really?

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