As mentioned above, Robin is not a common Japanese name. But "IF," by any chance, someone were named Robin in Japan, I think it could sound both.boy or girl.

I thought Robin was originally a nickname for Robert or Roberta so it was used by both a boy and a girl. By the way, there are also some Japanese names that can be used by both a boy and a girl, for example, Akira is usually a boy's name but there are quite a lot of girls having that name. Chihiro used to be a boy's name but today the majority of Chihiro's are girls. Jun,,, well this is a tricky one. I would say it's a tie.

Robin is also a boy's name in America. Batman's boyfriend is called Robin. Japanese girls have Japanese names, not American names. Robin is not a Japanese name.

Robin is not a common name in Japan. I guess it's American girl's name. Maybe you can see the girls named Robin in comic books. But in the real world, Robin is not for Japanese girls.