Fun fact: Hachi (or at least the character that was supposed to be Hachi) was originally planned to be a girl, but it didn't come out as a good idea at the end

Fun fact 2: If joker was at silver heart's age, he canonically would behave like him

Fun fact 3: The idea of joker first came out as "childish lupin the third buy in red clothes". After the personality was out, they figured they needed a little girl who follows him around going "Wow!" On what he does and that's how Hachi came

I can tell you all of this because twitter just showed an interview with the author and I went through Google translate to get a rough translation

Also: in an extra chapter he said that he had the choice between a sumo wrestling manga or a phantom thief manga. You probably knew what happened next