Josuke is very innocent and clueless, but very calm. I would imagine he has a medium-high voice, which can convey both intimidation, calmness, and the occasional kooky moment. At one moment he can be a child stuck in a young man's body, while another he can be punching a guy's organs out with no sense of guilt. Here we don't see much of his kooky side, but more of his calm side of things.