All deaths and disappearances are listed only as they are told in Tataridamashi-hen and apply only for the individual arc, not the overall series.
Deaths
Teppei Houjou, beaten to death by Keiichi Maebara, June 19, 1983.
Mion Sonozaki, killed by Kuraudo Ooishi, June 19, 1983.
Shion Sonozaki, killed by Kuraudo Ooishi, June 19, 1983.
Rika Furude, killed by Kuraudo Ooishi, June 19, 1983.
Satoko Houjou, killed by Kuraudo Ooishi, June 19, 1983.
Trivia
The deaths of Mion, Shion, and Rika are not seen until the opening of the first episode of Nekodamashi-hen. Furthermore, although Rena describes Satoko as being killed, Satoko's death is never shown.
References to previous arcs
When Shion blames Oyashiro for the continued suffering of the Houjou family, Rika is visibly upset. This is due to Rika's companionship with Hanyuu, the true form of Oyashiro.
Rika claims Keiichi taught her how easily fate can be changed. When Keiichi asks when this happened, Rika replies "it's a secret".