|Relatives, etc.|| Nobuko Izumi (Wife - Deceased)|
Shinichi Izumi (Son)
|Occupation||Magazine writer (formerly)|
|Anime debut||Episode 1|
|Manga debut||Chapter 1|
|English Voice||Rob Mungle|
Kazuyuki is a tall middle-aged man with a mustache and black hair that he keeps combed. He's normally seen wearing a brown button up vest over a green long sleeved shirt and blue jeans.
In the beginning, Kazuyuki is a rather laid-back person, seeming to go with the flow with any changes he notices that take place in Shinichi Izumi. Later on, however, after Nobuko Izumi dies, he gets depressed and develops a drinking problem.
Kazuyuki is first seen late at night, entering his son's room along with his wife after hearing strange noises. After witnessing his son on the floor with a cord wrapped around his arm, he asks what he's doing. Shinichi Izumi quickly tells him of the '"snake" that jumped into his arm, and goes to show him the hole left from it. With no hole or any noticeable injury, Kazuyuki asks Shinichi if he's on drugs, something Shinichi denies and Nobuko Izumi laughs at.
- The name Kazuyuki means "one" (一) (kazu) and "to go" (之) (yuki).
- Kazuyuki's surname Izumi means "spring, fountain" (泉).
- Kazuyuki was omitted from the live action movie.