The future. People who posess ESP abilities are becoming more and more common. While most use thier powers responsibly, there are those who use their abilities only for destruction.
An organisation called BABEL (Base of Backing ESP Laboratory) is set up to combat the criminal espers.
Five years after BABEL's inception, a trio of level 7 (designated the highest level of ESP power) espers are located and recruited into a special task team called "The Children"
Their field leader is a lieutenant named Kōichi Minamoto. His sincere belief is that the members of "The Children" Aoi, Karou and Shiho are little girls who should be protected, before they are level 7 espers.