CFUD AU Event! Awesome.
Leave it to me to pick one of the AU possibilities that would involve firearms. Toei cheated us out of a really hot thing: Kanna Mori, all militia'd up and dirty and with a rifle (you're looking to the bottom right), presumably hunting down Tsukasa for one reason or another. I am still bitter. I am taking it upon myself to get my way.
Anyway, the story goes something like this: the proper ending for Decade never happened. Instead, the Rider War got out of hand, forcing Natsumi to flee and learn how to fight while Decade started systematically picking off Kamen Riders one by one. She knows three things for sure: the Rider War she's had nightmares about has truly begun, Decade must be stopped at all costs, and that she may have to be the one to do it. She's convinced herself that the Kadoya Tsukasa she knew is no longer alive in there.
So she's become stronger! Obviously, she's no longer Kamen Rider Kivaara -- rather, she never was. But she's become kind of a heroine in her own right, and has thrown herself into hunting down Decade to destroy him before he can destroy all of the Kamen Riders, no matter what the consequence is to herself ... though he's already gotten to a fair share of them by now, and she's pretty sure she'll die again.
What This Means for Kamen Rider Folks: You might be dead! Um. I'll ask you if you tag me/before I tag you if you have any preference as to whether or not you've survived; Natsumi may or may not know but she's been trying to keep track of who is and is not currently a Rider Card. If you've survived, she'll be pretty insistent that you not go near Decade. Ever. If you're dead, anticipate shock and confusion. If you're Decade ... godspeed, she's armed. She won't be familiar with any Riders except the ones who appeared in her canon before Movie Wars 2010, including original Riders who became A.R. Riders (Kiva, Ryuki, etc.).
What This Means for Everyone Else: She won't know you, and she might be a little bit less personable than she was before. Maybe a lot less.
If you want to ask anything/plan anything/etc. let me know! I'm happy to oblige. Just ping or PM me, or comment here.