The train's diner car is decorated with golden wallpaper curved booths with oval tables to one side, and a bar opposite. Finn and Jake look out the train's hexagonal windows to see a beautiful, rainbow-coloured sky under an expansive mesa. "This is the DenLiner, destination: time itself. Every grain you see is a second that has happened and will happen." Tsukasa told the two. "Bet Prismo wishes he had a view like this." Jake commented. "[Why did you bring tourists?!]" Momotaros asked Tsukasa.
"[They're adventurers, and they're hardier than you think.]" Tsukasa explained. "Tsukasa, he mentioned something a castle?" Jake asked. Momotaros nudges Jake and points outside. As they move past a butte, they see a massive dark fortress lit by blue lights, with dark clouds looming above created by weather machine spires. "I recognize that architectural mess. There's an abandoned fortress on Ventara, the mirror dimension in Kit's world. It was built by General Xaviax." Tsukasa explained.
"[Turtle, Bear, and Brat are trying to blow it up, but they've run into a pinch.]" Momotaros said as the train turns towards the fortress. Three futuristic trains, blue, yellow, and purple, attack the fortress with lasers, axe rams, and a dragon-headed fireball launcher while being chased by giant dragonfly monsters. A walkie-talkie on a nearby table crackles, which Momotaros picks up. "[Senpai, these insects are keeping us away from the fortress! Over.]" a suave man's voice informed Momotaros. "[Tch. Do I have to do everything myself!? Over.]" Momotaros screamed angrily.
"[Momotaros, I have a plan to get in. Just set us down on the ground.]" Tsukasa told Momotaros. The DenLiner swoops down to the ground and the three heroes swiftly jump out. "So, what's the plan? Sneak into the sewers or something?" Finn asked. "That's how Kit and his friends infiltrated the place years ago." Tsukasa confirmed. Finn lifts up a manhole and jumps in, followed by Jake and Tsukasa.
Outside, the DenLiners continue to attack and evade the dragonfly monsters. Since Momotaros joined, they have had better luck defeating them with his missiles and bombs deployed from the train cars. Aware of their impending doom, the monsters drop off Gelnewts onto the DenLiners to sabotage them. Momotaros is piloting the DenLiner in its cockpit with a motorcycle when he hears stomping above. "[Get off my train!]" Momotaros screamed as he performs an aileron roll to shake them off to no effect.
Zervas monitors the battle outside from a massive circular screen in the middle of a room covered from top to bottom with machinery of unknown functions. He swipes away the holographic screen, revealing Another Zi-O, trapped in a cylindrical pod behind it. He hears a clang behind him and sees Finn prying open the door with his Night Sword. "Perhaps persistent is too light of a descriptor for you three." Zervas told them. "Here's how this is gonna go down; we beat you, we destroy Another Joe, and we get outta here!" Jake screamed.
"It's Zi-O." Tsukasa corrected. "I'd like to see you try." Zervas scoffed. "I'm quite confident we will. Seeing as you don't have an Advent Shield around the facility, the concentration of guards occupied with the DenLiner crew with none inside your base, and the fact you use a Visor for your attacks, I take it you're severely underpowered." Tsukasa taunted. "Correct. I spent all my resources towards finding this creature." Zervas said. "To bring Xaviax from the past?" Tsukasa asked.
"Not directly." Zervas said before throwing another energy ball at him. Finn bats the energy ball with the Night Sword, flinging it into a side wall. Zervas dashes towards them and engages Tsukasa, who defends with the side of his sword. "You two get Another Zi-O, I'll fight him!" Tsukasa yelled. Finn and Jake run to the pod, leaving Tsukasa alone with Zervas. He kicks Zervas away and slashes his chest.
"You're a formidable one. Who are you, exactly?" Zervas asked. Tsukasa puts on his magenta belt and takes a card from his book, one printed with the face of a magenta-coloured, green-eyed Kamen Rider. "I am Kamen Rider Decade." Tsukasa answered before flipping the card around to show an insignia resembling the Kamen Rider's face. "Henshin!" he yelled before inserting the card into his belt and flipping it closed. "Kamen Ride: Decade!" a macho voice announced from his belt.
A multitude of spectral figures surround Tsukasa before converging into him, materializing into magenta-and-black armour with an "X" crossing from his left shoulder to his chest, and the illustrated helmet. He takes his sword and comes after Zervas. "He's a Kamen Rider?" Finn said in surprise. "Would've been nice to know." Jake said before he is jumped by an Another Rider with a goblin-like face, wearing red-and-blue armour with an alternating colour pattern and a mechanical design. Finn quickly slashes it down the middle, powering it down and revealing it to be Princess Bubblegum.
"Ugh… Finn? Where am- Aaah!" Princess Bubblegum groaned before falling through a time portal. Finn and Jake watched her disappear before turning to Another Zi-O. "Tsukasa said they're all peeps we know. Who'dya think this is?" Finn asked. "Only one way to find out." Jake said. Before Finn could act, a time portal opens and an Another Rider appears, with gold-and-red dragon armour, a left hand replaced by a dragon's head, and branded "RYUKI" "3047" across its chest.
Zervas was knocked into a wall as it appears. "Finally!" he exclaimed. He gets up and takes a card from its belt before pushing it away. "It's mine!" Zervas screamed as he holds up the card. The card illustrates a clock, labelled "TIME VENT".
"Another Zi-O can only summon past Another Riders, so that meant he was only after Another Ryuki for its Time Vent card." Kamen Rider Decade noted. Zervas turns around and destroys Another Ryuki instantly, ejecting its host. "Finn? Jake?" BMO's voice said. Finn and Jake look to see BMO's reflection in the circular screen's hologram. "BMO?!" Finn and Jake said in surprise.
"I'm not BMO, I'm Footba-Aaah!" Football corrected before dissolving. "Time Vent." Zervas' Visor announced. He holds up his hand as a surge of electricity lights up the room. The lightning strikes Kamen Rider Decade and Jake, who keel over in pain. "General Xaviax will rise again!" Zervas screamed.
Finn is immune to the effects as he looks at Zervas with his sword drawn. "Not him! Another Zi-O!" Kamen Rider Decade yelled to Finn. He looks to the pod and leaps towards it to send an electrified slash, destroying the pod and Another Zi-O inside. The Time Vent card evaporates from Zervas' Visor, ceasing his attack. "No! I was so close!" Zervas panicked.
Back in Japan, Kamen Rider Zi-O, Kamen Rider Dragon Knight, and the Odd Jobs witness Another Blade and Another Gaim reverting to Finn and Fern before disappearing into portals. "I think Finn and Jake found him!" Kamen Rider Dragon Knight said in relief. "Let's hope they'll come back, wherever they are." Mary said. "They really should stop going on surprise missions to other universes. If Miss Campbell were still human, she'd have an ulcer with how many times they do this." Jerry commented.
In the Sands of Time, the defeated Zervas clutches his Visor stressfully. In place of Another Zi-O is Clock Bear, Doctor Gross' bear hybrid. It lets out a bear-like groan before it falls into a time portal. "All my work… reduced to ashes to a child!" Zervas screamed. He goes after Finn and Jake with a charged-up fist powerful enough to knock the Night Sword out of Finn's hands.
Jake stretches into a shield to block the attacks to Finn, but is punched in the face by Zervas. "Ow." Jake moaned. Zervas winds up his Visor arm to land an extra-powerful punch on Finn, who sets the Jake-Shield aside to punch it back with his right arm. The fists collide, causing the virtual skin on Finn's arm to flake and glitch. "Your arm's not looking too good." Zervas said, still putting his fist against Finn's.
"Ditto." Finn said before deploying his arm sword, cutting through Zervas' knuckles and his Visor. "Aaagh!" Zervas screamed in pain before keeling over. The dragonfly monsters outside evaporate into nothingness as the DenLiners stop in place. After this, Finn's arm falls off, glitching back to its default robotic form. "[And don't come back!]" Momotaros yelled.
"Day saved, great. Now let's go home." Kamen Rider Decade said. Discretely, Zervas inserts an Advent Card depicting a metallic whip labelled "SWING VENT" into his broken Visor. He shoots a cable from his arm into his ring-shaped computer. Instantly, the entire structure starts to rumble. "What did you do?!" Finn asked Zervas as he grabs him by the collar.
"Taking you home, though I can't guarantee you'll survive the trip." Zervas answered. The fortress is quickly being engulfed by a blue energy field. The DenLiners line up to watch this strange event. "[I think we should leave.]" Momotaros commented before the trains disperse to avoid the bubble. The fortress is consumed completely and is sent to a crater in Japan, formerly known as central Shibuya.
Sougo, Kit, and Super Megaforce run to the site where they see the fortress in a charred state, surging with residual energy. "That's a Karshian fortress, like Xaviax's." Kit noted. Suddenly, a mirror portal manifests and emerging from it is Sougo's edgy partner and an older white man with similar black hair, wearing a black jacket with a golden, wing-shaped logo. "Kit, what happened?" the older man asked. "I think Finn, Jake, and Tsukasa did something, Len." Kit responded.
"You didn't tell me the Destroyer of Worlds was here." Len commented. "Sorry. I was busy being attacked by an orange samurai." Kit shrugged. A veil of rippling reality manifests before them, and tumbling out are Finn and Jake, carried by Kamen Rider Decade. They stand up and dust themselves off before looking to the others. "You guys made it! Out of whatever happened, but you made it!" Pink Ranger said.
"Super Megaforce? You guys sure are late to the party." Finn said. "Am I missing something?" Geiz wondered. "All you guys need to know is that we saved the day." Jake said. "What about Zervas? Where is he?" Kit asked. "He likely died in the teleportation." Kamen Rider Decade said as he removes his belt, reverting to Tsukasa.
"In any case, we have you to thank for stopping him, Tsukasa and…?" Len said to the three heroes. "I'm Finn, and this is Jake. We're adventurers, and we're glad to have helped." Finn introduces himself. "Your mom told us you were missing… again." Red Ranger said. "After some scanning around the place you were last seen, we had Doctor K bring us here." Blue Ranger explained. "She said hi, by the way." Black Ranger said.
"[You're gonna have to explain everything to me later.]" Geiz said to Sougo. "Well, Tsukasa, it's been-" Finn said to Tsukasa, but finds he disappeared. "[Just like him to disappear like that.]" Sougo commented. "If we're all done here, your mom is waiting on a two-minute hug from you." Red Ranger said to Finn as a Multiverse Bridge opens. "It's been great meeting you, Kamen Riders." Finn said to the heroes.
The heroes walk through the portal and arrive in Hub City. "Jake, I remember where I first heard about Kamen Rider: the statue from our mission in Japan!" Finn recounted. "I remember that one. Too bad we didn't see the guy the statue was based on." Jake added. "Whoever he is, he should be proud of these newer guys." Finn said. Before the portal fully closes, an armoured hand emerges.
Back in the Kamen Riders' universe, Tsukasa parks his magenta motorcycle at a curb. He dismounts and faces a photo studio built out of a house named "HIKARI STUDIO". He enters the front door with a smile. "Tadaima, Natsumikan." Tsukasa greeted. Following this is an audible jab, and Tsukasa forcibly laughing.
THE END