Phi Brain: Saigo no Puzzle  

ファイ・ブレイン 最期のパズル

Daimon Kaito is a high school student who enjoys solving puzzles. The president of the student council assigns him a mobile device that leads him to an underground ruin within the school. Along with his girlfriend Nonoha, he takes on the challenge of solving an "unsolvable puzzle" hidden in the ruins. However, what they thought was just a puzzle turns out to be "The Puzzle of Sage," created by the dangerous black society known as POG. Despite successfully solving the puzzle, Daimon and Nonoha's victory marks the beginning of a battle against POG, as they must now face off in a series of challenging puzzles.