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Yonemura Hisaku, an ordinary high school student and head of the "reasoning club", is facing the crisis of the club's abolishment. Just when he was about to give up because he was unable to continue running the reasoning department, he suddenly received a mysterious "commission" from his class teacher, Mr. Xiaoshan. The reward for the commission was to help Yonemura revive the reasoning department! However, Teacher Xiaoshan's commission was too fantastic, and Yonemura also discovered a secret hidden in the school that had not been discovered for many years...