Traditionally, movie-exclusive "dark" riders (i.e., Orga, Caucasus, Eternal) are based on the titular rider of the franchise. However, G4, the first movie-exclusive rider stands out like a sore thumb, being based on the secondary rider instead of the titular one. However, he IS based on Agito in a way - while he does share the same similarities with Kuuga, design wise he has elements in common with Agito as well - since G3 was meant to combat the Gurongi, G4 was likely developed with the purpose of battling the Overlords, but was scrapped in favor of the G3-X system in-series...much like how originally, Agito was going to be a sequel to Kuuga.
When the Overlord sets off his Scorpio suicide plague near the end of the series, there is no indication that it is confined to Japan. Who knows how many millions of people died before he was stopped? Especially given that some of the Scorpios must have been driving buses or planes when the compulsion hit...
