Phi Brain: Saigo no Puzzle

A high school student passionate about puzzles receives a mobile device from the student council president, which directs him to a hidden underground ruin beneath the school. Alongside his girlfriend, he attempts to solve a complex puzzle, only to discover it is part of a series known as "The Puzzle of Sage," crafted by a secret organization called POG. Although he successfully solves the puzzle, it marks the start of a conflict involving a series of challenging puzzles set by the group.