One thing I do appreciate the Heisei Riders vs Showa Riders movie for is the fact that at heart, the plot is actually quite poignant for a team-up movie. And for me, this was the key scene. I will try to keep the spoilers general, but anyway…
SPOILER WARNING FOR: OOO, WIZARD, FAIZ, GAIM, DOUBLE, DECADE AND KIVA.
I find it interesting that the Heisei riders that they choose in this scene are the ones that are most intimately familiar with death and regret.
OOO: Eiji does the little guilty look to the side, because not only is his whole character arc based on regretting the death of the little girl, considering the end of OOO, he might very well have been paving the way for Badan with his future as well.
Wizard: Haruto is also formed by the death of his parents, but even more, by his whole character arc with Koyomi. Breaking the rules of death is something he is intimately familiar with.
Faiz: Takumi is most likely the one most familiar with death of the whole bunch, and the movie goes into that quite a bit (which I loved).
Gaim: Kouta has been the most outspoken when it comes to opposing death, having been the cause of both Yuua and Hase’s demise.
Decade: Tsukasa was dead, and supposed to destroy all the alternative rider worlds. Him being brought back by his friends is exactly the kind of crime that the Showa riders are talking about
Double: Not only is Shotaro’s whole personality formed by the death of his mentor, he is here as Joker, not Double, which means that time-wise this is at a time when he really wants to reverse death.
Kiva: Wataru was prepared to risk the entire fabric of time just to make sure that someone he loved didn’t die, and then… well, someone he loved died anyway.
One might argue that the riders not present are also formed by death, but if we have a closer look at the remaining eight, not at all to that an extent:
Kuuga: No reversing death here. Just death, pain and killing.
Agito: Death/resurrection is not a major theme there. People die and are grieved, but that’s it.
Ryuki: Well, let’s just say that Shiro is not a rider.
Blade: Death… might have been the kinder choice.
Den-O: Time and memories… but not death.
Hibiki: Accepting death is something you have to do.
Kabuto: Not much to do with death there, more about identity and family.
Fourze: Gentaro knows about death, but his whole experience with the power cosmic sidesteps the whole underworld thing completely.
I would love to know enough of the showa riders to see whether their inclusion is as thought through as the Heisei ones. I know that Black would be there, because his whole arc is about accepting the inevitable death of his brother Shadow Moon, but alas, I have not seen the other shows yet.
Kabuto did deal with death. His parents died. And many more people. And its not just death. It’s a person being imitated and then being killed. It’s having the murderer parading around as the decesaed. It’s about whether or not Hiyori can even be considered his real sister considering his sister died. Death is important in COMBINATION TO identity and family. Mortality. Existence.