Light Novel The old man and the high school girl looking up from the window of Ethos Famitsu Bunko

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A mystery solving consultation by an old man and a high school girl who share a secret starts! A super negative but energetic high school girl, 憂海 瀬宮, and a 老教 teacher, Genzo Toyohashi, who shares a secret in a strange way. The topic of their lunch is always a small mystery in the school! 憂海 is going to show you a theory against the old man who seems to have understood everything? Will she be able to solve the worries of the most beautiful senior students in the school and the mystery of the closed-door affair! Sweet and sour youth mystery solving consultation by old man and high school girl!