Japanese literature I wonder where we made a mistake

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Japanese literature
Hitomi lived a normal life in a peaceful country town surrounded by close family, friends and neighbors. However, everything changed because of the annual Autumn Festival Day. Someone poisoned the Sweet Red Bean Soup served at the festival, and many people died. Shuichiro and Ryoon, who were Hitomi's childhood friends, became family members of the victims. To know the truth of the incident, Hitomi began to investigate.