Hiro is the biological father of Kimi Watanabe-Finster. He is from Japan, like his ex-wife, Kira, and his daughter Kimi. Kimi became very interested in her family history in "Memoirs of a Finster". 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.
Hiro is a light-skinned Japanese man who wears a business suit and wears glasses. He has purple hair/eyebrows and looks similar to his daughter, Kimi.
- He was first mentioned in the the All Grown Up! episode, "Memoirs of a Finster".
- In "Memoirs of a Finster", Kimi is seen talking with Hiro on the phone about her family and wanting to know more about his side of the family so she can complete her family tree.
- It's possible that Kimi filled her father in about her time living in the United States and the current neighborhood she resides in, which means he might have some knowledge about Z.