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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).
Although he was 70 years old, he did not act it, and regularly flew around the Main Order Room in "Jet-Roller" roller skates (which also provided him with the "Reo Lariat" attack, in which he sped toward a target - that is, his older brother Liger - and smashed his elbow into him). He was not beyond going into the field, either, and in Number 15 piloted LinerGao through a manual Final Fusion sequence (and continued to ride it through GaoGaiGar's subsequent fight with EI-15).
Reo met his final fate piloting the Assault Reconnaissance Cutter Murakumo, in Jupiter orbit during GGG's final battle with the 31 Machine Primevals; Murakumo was destroyed in the process and fell into Jupiter's gravity well, where the spirit of Reo himself was saved by (and became one with) The Power generated by the planet. There, he was also reunited with his wife Kizuna (who had herself met a similar fate). As GGG's final battle continued, Reo and Kizuna managed to release a vast amount of The Power from Jupiter, allowing the Mobile Unit to absorb it and destroy the remaining Primevals.
During the opening of the seventh episode of King of Braves GaoGaiGar FINAL, a photograph of Reo and Kizuna is seen, with Jupiter in its background; this alludes to the viewer that Reo remains "alive" - albeit in spirit form - within Jupiter.