This story is based off a comment from chapter nine in Kamen Riders together when it's mentioned FBI agent Taki Kazuya does stupid things when he honestly thinks that there aren't any Kamen Riders around. What you recognize I don't own and while thoughts will be in italics while I normally astrik foreign languages due to the fact that the story will mainly be based in Japan that will not happen this time however I will denote when the main character finally is in Japan so that there's no confusion
Taki was in his office when he heard one of the FBI agents mention Japan and since he knew people in Japan and he wasn't really working on anything important at the moment he decided to listen in on the conversation just to get an idea of what was currently going on hoping that things were currently calm enough that Kamen Riders weren't needed
"So Japan has some issues huh?"
"Yeah, but here's the thing none of those...uh masked heroes that help on a regular basis are around, apparently almost all of them went up against one of the enemies and were killed, there are probably I think two still alive but if they are they are keeping an extremely low profile because they haven't been in the news in a while"
"How long is a while?"
"It's been a full month since Fourze and...Gaim I believe they're called have been heard from and the enemy declared they killed everyone up to Fourze and they also killed Wizard"
"Will two of the masked heroes even stand a chance against such a formidable enemy?"
That's when Taki speaks up
"Of course they will, they're Kamen Riders they won't give up without a fight, and if the other Riders are dead then they gave the enemy a fight to remember as well"
Just then a shout was heard
"Something's up in Japan on live TV!"
Everyone runs to the TV and Taki sees Fourze and Gaim fighting hard when suddenly there was a huge explosion where the Riders had stood and when the smoke cleared there was nothing left but their drivers
"The masked heroes are...dead"
"Kamen...Riders"
Everyone could see that Taki was in shock
"Kazuya are you okay? Kazuya"
"What do we know about Japan's current enemy?"
"Not much but in all honesty since it doesn't really constitute a threat to national security we don't really pay attention to all the monster attacks that happen over there"
"That's a mistake that's going to cost us soon if we don't act quickly because those organizations are actually world wide, they are just more prominent in Japan because there's a more visible resistance, though before their deaths the other Kamen Riders would go around the world in case of hot spots as well, at least if they were old enough and had a job that would allow it. I'm going up to speak with the director in the meantime try and find out everything you can about the current enemy, reporters are a good source over there but don't trust any reporter calling themselves Ichimonji Hayato, at least until you can have them talk to me personally"
"Why?"
"Just do it"
"Yes sir"
Taki then heads to the directors office and knocks
"Come in"
With permission Taki walks in and the director knowing he's of Japanese decent and had been in Japan for a bit before several years earlier always talked to him using the Japanese version of his name if he did use his full name and also whenever he introduced him to anyone if at all possible
"Taki what can I do for you?"
"Request permission to go over to Japan to gather needed intelligence in person"
"Denied, I'm sorry Taki but the FBI doesn't want to take that chance right now"
"Then I request an indefinite leave of absence"
"What for?"
"Sir some of my friends are over there I have to see for myself if they're okay or not"
"Granted, however any intelligence you bring back gathered from you personally will not be used is that understood?"
"Yes sir" (thinks) "unfortunately for you sir that's no longer the plan seeing as how you denied me the gathering intel leave I have to do something else and if you ever find out you're not going to like that you gave me permission to leave the country"
"However understand this you may not even be able to get into Japan depending on how quickly things collapse"
"Don't worry sir I have my ways"
"Taki what are you talking about?"
"Easy sir, air travel may soon be banned however it's a lot harder to keep an eye on the see"
"That's true however if you don't enter through official points of entry we're going to have to deny you even exist if you're found with your FBI identification"
"That won't be a problem sir because I'm handing in my ID and gun before I leave since I will not be there in an official capacity"
"Understood, I'll expect them before you leave the country then"
Three days later Taki was on a boat headed to Japan, he knew it would be several weeks and as such while on the trip he gathered the most up to date intel on the enemy whenever he could and he also did his best to see if any of the Riders had actually survived and were now simply laying low and hiding but every time he got his hopes up they were dashed quickly. Finally he reached Japan and then started looking for the enemy base and once he found the main headquarters he started gathering intelligence once again so as to try and sneak in and do damage from the inside. While doing so he managed to find a few people who took him in knowing that if they were alive and in their civilian identities that's what the Kamen Riders would do
"Iruma are you heading out again?"
"Yes I am Izumi Shingo-san"
"How many times do I have to tell you it's Shingo"
"Sorry, even though it's been three weeks it's not something I can get used to, at least not until later if at all"
"Why not Iruma?"
"If I can ever explain it I will but not now"
"Fine, be careful"
Taki trades places with one of the people who regularly went in and out that day and actually got pretty far while also occasionally doing minor things to sabatoge the mission of the enemy when finally he was discovered and brought to the leader
"Did you honestly think we wouldn't notice you sneaking into our headquarters?"
"Actually no but I was hoping to last longer than I did at least"
"That will never happen we're too well guarded"
Taki is then taken to a cell and for three months he escapes several times despite his injuries from interrogation getting further each time when one day something changed, something that Taki would be very grateful for though also knew he would regret his decision to come all things considered. That day Taki was bound up tightly and blindfolded and then taken out of the cell. After several twists and turns the blindfold was finally taken off and the binds were cut and he was shoved into a new cell
"Enjoy your stay with your new companion considering he's all but insane now"
The door is slammed shut and Taki looks around and sees one person in the corner rocking themselves constantly and then very softly he heard the words that were being said by the person's very hoarse voice
"Dead, all dead, my fault, all dead, my fault, dead, all dead, my fault, my fault, all dead"
In varying order those three phrases were said for several hours and then afterwords were the names said
"Hayato, Shiro, Keisuke, Daisuke, Shigeru, Hiroshi, Kazuya, Ryo, Kotaro, Yusuke, Shoichi, Takumi, Kazuma, Hibiki, Souji, Ryotaro, Yuto, Momotaros, Urataros, Kintaros, Ryutaros, Deneb, Wataru, Tsukasa,, Shotaro, Philip, Ryu, Eiji, Shintaro, Akira, Haruto, Nito, I'm sorry, my plan failed I am so sorry"
"Takeshi...Takeshi it's Taki"
Unfortunately for the next three days Hongo Takeshi doesn't hear Taki but eventually he does succeed
"Ta...ki you're supposed to be in America"
"And you're supposed to be dead, all of you"
"All of us?"
"Yeah, shortly before I came here they got Fourze and Gaim as well
"Gentaro, Kouta, they're gone as well?"
"Yes...don't go inside yourself again please I need someone who's with me so that we can escape"
"What are you even doing here?"
"Well I kind of heard all the Riders were dead, and actually saw Fourze and Gaim fall on live TV so first I decided to get first hand intel on the enemy so that America would be prepared then after that was denied I decided to come here and take down the enemy before they decided to try any overt attacks on America or anywhere else in the world, make them focus here in Japan like they always do as a means of buying the rest of the world time"
"All of this because you thought all of us were dead?"
"Yeah, but now we can escape and hopefully I can find the people who I stayed with still at their place and we can stay there under assumed names due to the fact that as a safety feature I decided not to give them my name just in case"
"Then we'll do that"
They eventually escape and make it back to the Izumi place and they continue fighting from there. Eventually the two find out that the other Riders didn't die like thought but went into deep hiding instead and eventually they won though only Hongo Takeshi and Ichimonji Hayato would ever know what Taki did because after they escaped Taki got himself captured again and this time it was Hayato who would be doing the rescuing. The reason Taki was captured again was because he stupidly decided to take on a factory by himself without letting anyone else know about it only to discover it was more fortified then he thought, though he only did that because of the fact that he thought once more there weren't any Riders due to the base being blown up with everyone in it or so he thought not knowing that they all had other missions at the time