Kaita - lover of puzzles, who recently transferred to the school called Root Academy. He is selected as a candidate for Phi Brain for his extraordinary mental abilities. Once, he and his childhood friend became Nonoha solve "unsolvable puzzle" hidden in the underground ruins near the school. They focus on the mobile device that Kaita received from the President of the Student Council. Puzzle, life-threatening, the creation of a mysterious organization known as POG. When he decides to puzzle, he termed the "solver". Together with other solvers and Nonoha, Kaita fights with POG.