The former Chief Scientist of the Gutsy Geoid Guard, responsible for all of its G-Stone technologies. Father of Guy Shishioh, he appeared on the surface to be somewhat flippant about his son's involvement in GGG (though as a father, the only reason he let Guy fight was his request to do so). During the opening of the seventh episode of King of Braves GaoGaiGar FINAL, a photograph of Leo and Kizuna is seen, with Jupiter in its background; this alludes to the viewer that Leo remains "alive" - albeit in spirit form - within Jupiter.