Heiji is the son of Heizo Hattori, chief of the Osaka Police Department, and his wife Shizuka Hattori. Heiji wants to become a detective, and his father is very supportive of this, helping him solve tough cases. However, his father has given him tough love, though mostly for the sole purpose of having Heiji get him to bring a suspect out. Heiji is also very skilled in kendo and has become a favored tournament contender for his school.

Even while solving a case, Heiji tends to be lighthearted and good-humored, preferring to work through it with a grin on his face. He is a big fan of baseball, and is most of the time shown wearing an Osaka cap, to support the local Osaka baseball team.