15화: 마야가 아플 때까지 아야가 친구들과 함께 고등학교의 미스터리를 조사하다

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Aya is told to investigate the 5 mysteries in the High School, so (as she is afraid of ghosts) Akira, Kengo and Shirogane helped her. All those mysteries prove to be false, but after they thought it's all done, Maya falls sick and goes to a doctor. The doctor is deeply unsatisfied with his current position, being in a high school and in a university treating mild sickness. He is possessed by Kokuchi. (Source: Wikipedia)