Four years ago, during the dam incident, young police investigator Mamoru Akasaka comes to Hinamizawa to find leads to a child kidnapping. After hearing an enigmatic warning from a younger Rika, Mamoru becomes suspicious of some of the townsfolk.

Akasaka and Oishi find the kidnappers' hideout and rescue the boy. After discovering that their efforts were in vain because the perpetrators' demand was already conceded, he realizes the real meaning behind Rika's words to him.