Hiro is the biological father of Kimi Watanabe-Finster. He is from Japan, like his ex-wife, Kira, and his daughter Kimi. It is known that Kimi became very interested in her family history during "All Grown Up!". She was seen by Chuckie talking on the phone with her father in her bedroom, solidifying that they had some sort of a relationship. Her father still lives in Japan. Kimi sees him in the All-Grown Up episode Trading Places where she meets her new baby half-sister, Kiki Watanabe. As Kira married Chas in Rugrats in Paris, it means that Hiro and Kira are divorced.