The Hill Dyed Rose Madder

Season 1, Episode 3: The Scream of Bizzare Colours

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Jun'ichi's teacher Seijirou Sugishita goes missing in an abandoned portion of the school. The student council president Mitsuki Siina enlists Jun'ichi and his friends to search for him in the abandoned school building. While searching Jun'ichi and Yuuhi fall down a trap door into a pit. The two are forced to work together to try and get out, but are unable to escape. In the same pit Mr. Sugishita wakes up from under a blanket and the trio are found shortly afterward by Minato.