A long time ago, Dan Moroboshi and his brother Rei were normal alien children whose parents were interstellar diplomats. Their parents were killed by terrorists as a warning, and Rei was kidnapped. Dan could do nothing but hide and watch in terror. At some point, Rei's mind was removed from his body, which was used as a vessel for a Star of Darkness member whose body was damaged beyond repair.
Years later, Rei emerged on a broadcast from the Star of Darkness, shocking the SSSP and especially Dan.
During the battle in New York, "Rei" was the first Star of Darkness member to arrive on the scene, and used devices to summon the others. Dan went after his "brother" and learned that it was simply his body being used by another person. With no more reason to hesitate, he swiftly decapitated the terrorist to preserve what was left of Rei's dignity.
- He shares his name with a protagonist in the Ultraman Series, but their relationship beyond that is unknown at this point.
- Rei is completely absent from the anime adaptation's storyline.