Takashi Kaidō (海堂崇 Kaidō Takashi) is the biological father of Haru Kaidō, Aki Kaidō and Shima Kaidō. He was married with Haruko Dieckmann and he had Haru as their son. Unfortunately, Takashi and Haruko got divorced when Haru was still young. Haru stayed with Haruko in Alberta, Canada, until the age of eight, when he moved in with Takashi and Ruri Kaidō (Takashi's new wife). Takashi and Ruri had twin sons named Aki and Shima.
During ride back home after picking up Haru from the airport, they got into a car accident, and Takashi and Ruri both died.