Okay, this is how the Mutually Fictional works out.There are two choices, depending on which of them is the "real world". Option One: Nadesico is "real", Gekiganger is fictional
Joe Umitsubame came back to life because of the existence of Martian Successor Nadesico.Episode 2 of Nadesico shows Akito and Gai watching Joe's death scene. But in episode 14 of Nadesico, Joe is still alive while watching episode 14. This must mean that the Nadesico writers in Gekiganger's world decided to have Joe die in the Show Within a Show while he was still alive in reality! The Gekiganger team must have complained to Xebec about this, so near the end of the show they decided to refer to Joe coming back to life... and through the magic of anime, it actually happened. It would be a neat reversal: in Nadesico, anime causes a lot of the problems in the series, whereas in Gekiganger, it saves the world.