Heiji Hattori/Relationships

Conan Edogawa/Shinichi Kudo
Heiji acts rather brotherly towards Shinichi, even going so far as to pretend to be him on various occasions, so no one figures out that Shinichi and Conan are the same person and was second person who figure out Conan and Shinichi are one and the same.

Of course, this might also be to make up for all the times Heiji calls him Kudo, which has nearly given Shinichi away multiple times. Heiji can be a little bit worried for Shinichi when he gets into trouble and in a life or death situation.

Kazuha Toyama
Heiji and Kazuha are childhood friends.