Deep Water <Shinen>

A 13-year-old girl named Aki Kasuga was discovered at the scene of her parents' deaths near Lake Ezu, close to Kumamoto city, by her younger sister and detective Toru Takahira. The cause of the incident remains unclear. As a minor, Aki entered a reintegration program and adopted the new name Sei Kamihara. Six years later, another death occurs in Ezu, this time involving a young girl. A week after that, multiple animals in the zoo are found dead. The events appear to be connected in some way, but the nature of the link remains a mystery.