(Musical Chairs Chapter/Whirlygig Chapter)
Wiki description first.
At first glance, this additional "Question Arc" is a retelling of Onikakushi-hen. However, this chapter in fact contains the events of Watanagashi-hen. After learning the secrets of Hinamizawa, Keiichi decides to ignore everything and enjoy his peaceful school life; this action leads to a tragic series of events. Shion Sonozaki is the villain of this chapter, while Mion becomes the victim.
In this chapter Keiichi decides to ignore everything and live normally. Unfortunately, this results in a situation similar to Watanagashi-hen's/Meakashi-hen's events, except we do not see them happen, and Yakusamashi-hen's ending, with Mion in Satoko's place.
