I don't own Fate/Stay Night or Kamen Rider and they belong to their respected owners.

Shirou ran as Zi-O to assist Geiz who was being attacked by his "follower" from the future. Who came to kill Geiz and Tsukuyomi. But before he could help Geiz, Shirou was stopped by the man who ate his dinner and was holding a magenta Driver.

"You're that guy who ate my dinner," Shirou said.

"I'll be your opponent," Tsukasa said as he placed the Decadriver on his waist forming a belt.

He opens his driver and takes out the Decade Rider Card. He holds in front of him tapping it a little.

"Henshin," He says as he inserted the card into his Driver.

KAMEN RIDE: DECADE!

He henshin into the magenta warrior, Kamen Rider Decade. He took out his Ride Booker into sword mode and started attacking Shirou. Shirou started dodging his slash but always got him before being to the wall by Decade.

"Please stop!" Shirou pleaded. "I have to save Geiz!"

"Can't let you," Decade said.

Before he could do anything he was slashed in the back by a sword. The hit made him let go of Shirou and stumble back a bit. He saw it was Saber who attack him.

"You would not harm my master!" Saber declared.

"So, now you got your Heroic Spirit to help you as well?" Decade sighs.

"Thank, Saber," Shirou says before looking at Decade. "Why are you getting in my way?!"

"I don't know? Let me think of a reason," Decade said as he charged at the two.

Decade swung his sword but was blocked by Saber. Decade blocked Saber attacks before kicking her in the stomach and pushing her away. Decade takes out the Build Rider Card before inserting it into his Driver.

KAMEN RIDE: BUILD! HAGANE MOONSAULT! RABBITTANK! YEAHHH!

Shirou was shocked to see Decade turned into Build as Saber was curious about this form. She never met Sento when he travels to 2017 but she has seen the Build Armor.

"Build?" Shirou was shocked. "In that case…" Shirou takes out the Decade Ridewatch.

D-D-D-DECADE!

Decade charged forward and dodge a swing from Saber before slashing her across the chest making her stumble back. Decade swing at Shirou who blocks it with his arm while inserting the watch into his Driver and spun it.

The holographic cards appeared in front of Zi-O pushing Decade back.

ARMOR TIME! KAMEN RIDE! WOW! DECA~DE!

Zi-O gains the Decade Armor while the real Decade looks at him with a mild curiosity, "That's my watch isn't it?"

"And I'll use this," Shirou brought out the Build Ridewatch and inserted it into the Decade watch slot and spun his Driver.

FINAL FORM TIME: B-B-B-BUILD!

Now Shirou gained the Build Sparling form. Decade, Zi-O, and Saber charged at each other fighting, dodging with punches and sword slash. Zi-O and Decade both jump up and ready to use their finishers.

FINAL ATTACK RIDE: B-B-B-BUILD!

B-B-B-BUILD! FINAL ATTACK TIME BREAK!

They used their respected forms rider kicks but Zi-O has the advantage as Build Sparkling was stronger than the Build default form. Shirou kicked overpowered Decade, sending him stumbling back.

"I see…" Decade says he opens his Driver to return back to his default form. "Perhaps this form is better."

KAMEN RIDE: DECADE!

Tsukasa changed back to Decade. Decade charged forward to attack Shirou. What Shirou didn't know was that Decade was created to defeat all Kamen Riders.

Kasshine looks at the fight seeing his king being attacked, "Waga Maou!" He cries out leaving Geiz to assist his king.

Decade was about to be slash at Shirou again but was blocked by Kasshine trident and being pushed back by his trident.

"Is this another servant of yours?" Decade asked.

"No! You got it wrong!" Shirou denied.

"What do you mean?" Decade asked.

"Help me, Kadoya Tsukasa," Geiz says. "Let's put an end to Zi-O right here."

"Geiz, he's working for the Time Jackers!" Tsukoymi came in shouting.

"Yeah, do you even hear yourself, baka?!" Rin shouted.

"If it leads to defeating Zi-O, I'll take help from an enemy," Geiz said. "Will you help me as well, Archer?" Geiz looks at the red servant.

"...Yes," Archer said as he walks to Geiz's side.

"Archer what are you doing?!" Rin questioned her servant.

"You've seen what's happening out there, right," Archer says. "I couldn't believe it, this guy becoming a demon king but now… I believe Geiz is right, Emiya Shirou needs to be defeated."

"Dammit, Archer, don't make me use my command seal!" Rin shouted.

"Rin, save it because I will win the Holy Grail War for you but this is one thing I have to do," Archer said.

"I knew we shouldn't trust you, Archer," Saber hissed at the red servant.

"Let's go!" Geiz told the two.

Archer faced Saber as Kasshine tried to block Geiz but was pushed him aside and Shirou blocked Geiz Zikan Zax with his arms.

"Stop I wanted to help you Geiz!" Shirou shouted.

"I don't need to be saved by you!" Geiz remarked, he was about to hit him again but was pushed back by Kasshine.

"Stop it!" Shirou yelled out to Kasshine. But was blocked by Decade as the Magenta Rider continued his fight with him. Shirou can't believe this happening. He needs to help Geiz but he is blocked by Decade and Saber was busy with Archer. He knew Tsukuyomi and Rin can really beat Kasshine.

"It seems you're still in shock," Decade commented.

"Shock?" Shirou looking confused.

"Don't you get it? Geiz isn't your comrade," Decade said as he looks at the Red Rider and the robotic servant before looking back at Shirou. "Maou, your follower is."

"That guy is no follower of mine!" Shirou shouted back.

"Waga Maou," Woz's voice came from behind him. "It is about time you acknowledge it for yourself?"

"Step back Woz!" Rin said reading her circuits at the prophet.

"I just want Waga Maou to continue his path of conquest," Woz told her. "That is the version I know of him."

"No!" Shirou denied. "There's no way I'd order Geiz or Tsukuyomi's assassinations and the destruction of the world! I aim for the ally of justice!"

"I see," Decade said. "Then why don't you go see…"

Shirou turns to Decade confused about what he meant and turns back to see a Dimensional Wall that appeared behind him.

"… your future self," Decade has his Ride Booker in gun mode and aims at Zi-O. Decade fires hitting Shirou making him fly back into the Dimensional Wall.

"Shirou!" "Emiya-kun!" Rin and Tsukuyomi follow him into the Dimensional Wall.

Saber sees this and pushes back Archer to follow them as well. As Dimensional Wall closes Decade slashes Kasshine back pushing him away from Geiz.

"Let's go!" Decade grabs hold of Geiz dragging him away from the machine.

~/~

Shirou landed and de-henshin as he felt rough around him. He looks around to see dirt, rubble, and sand around him, there was hardly any plant life.

"Shirou!" Call out Tsukuyomi with Rin and Saber behind her.

"Where are we?" Saber asked.

"My home, the year 2068," Tsukuyomi answers.

"2068?!" Rin looking shocked.

"Yes, fifty years from your time where Shirou reigns as demon king."

"Is that me?" Shirou asks as he looks at the statue of him of his first henshin and surrounded by nineteen Kamen Riders. He takes a close look to read the plaque, 'Monument of Emiya Shirou's first henshin.' This can't be real.

Shirou begins to walk away from the girls.

"Where are you going?" Rin questions him.

"I want to see what this era is like," Shirou said.

After a twenty-minute walk, they finally found people in a refuge compound. They look around and the mages and servants did not like what they see. This was humanity's future. The sense of losing hope, faith, happiness.

"All these people… are suffering because of Ohma Zi-O?" Shirou asked.

"They're probably happy to be alive," Saber commented.

"Yes, they are," Tsukuyomi says before facing them. "The human population is half of what it is in your time."

The sentence broke them. Half of humanity gone. This is a nightmare.

"No…" Shirou didn't want to believe it.

Before anyone could do anything a scratch was heard as Ryuki's contract monster Dragreder came down on them spinning in circles around them. People screamed and before Saber could do anything they were transported to somewhere else.

They look around to be a plane land with a green with the brown dirt. They finally notice a throne with an old man sitting in a chair with his face covered by blinds.

"Someone is… there" Shirou says.

"That can't be…" Saber's mouth felt dry.

"... But it is," Rin says.

"Let me tell you a dream of a day where I was surrounded by fire. I wake up to see the world being destroyed by grotesque machines. With everyone dying, all I could do is stand and watch." Ohma Zi-O telling the story of the dream which was making Shirou breathe rapidly. "That's when a man appeared and told me, "You are a fledging king. You have a mission to become king and save this world from destruction." then I woke up to the smile of Emiya Kiritsugu."

"It's the same as my dream," Shirou said as he begins to lose his breath. He thought it was a lie. That Geiz and Tsukuyomi made a mistake but it was true he was the Demon King Ohma Zi-O. "This person is…" The blinds begin to role up until it was all the way up showing the old man's face. "...me." Shirou whimpered.

"Ohma Zi-O…" This was the first time Tsukuyomi seen the Demon King out of his suit.

"Emiya…" Rin couldn't believe her eyes.

Saber knew those eyes anywhere, even in old age she knows what her master looks.

"Why are you surprised, my younger self," Ohma Zi-O chuckled. "Don't tell me you were in denial?"

"You lie! You are not my master! He is a man on the side of justice!" Saber shouted at the man trying not to believe it.

"While I don't support his ideal… The Shirou I know said he would become the greatest and kindest king," Rin added.

Ohma Zi-O just laughed, making the others shiver a bit, he opened his arms, gesturing to himself, "Saber, Thosaka have you not seen what I've become, I'm the greatest and kindest king!"

"Then I should defeat you now and save this future!" Shirou shouted.

"Shirou, no!" Tsukuyomi tried to stop him.

Shirou just pushed her aside and he placed his belt onto his waist and inserted his watch on the right slot and spun the belt making him transform.

"Henshin!"

RIDER TIME! KAMEN RIDER ZI-O!

Shirou got his Zikan Girade in gun mode and placed the Fourze Riderwatch in the weapon's slot.

FINISH TIME: FOURZE SURE SURE SHOOTING!

Shirou shoots a barrage of missiles at Ohma Zi-O. The missiles hit the old man creating a large explosion. As the fire and smoke ceased all the show was the Golden King, Kamen Rider Ohma Zi-O.

"Impossible," Shirou looked in shock.

"Hmph, how nostalgic," Ohma Zi-O says as he used hi telepathic power to push Shirou backed.

"Shirou!" Saber cried out to her master thrown like a ragdoll.

Saber grip her sword and charge at the demon king. Even if she felt a strong surge of power coming from him she wasn't going to stop. She jumps up to her sword above her head ready to strike him down.

Ohma Zi-O holds his hand up, freezing Saber in place as her sword is inches from his face.

"My former sword, how nostalgic to see you ready to cut down an enemy trying to hurt me," Ohma Zi-O said as he began to raise his fist which was covered in golden energy. "But for me, I don't need such protection with the power I have."

The golden king gave one good single punch at Sabre's stomach making her grunt and sent her away and stumbled to the ground beside the others. Rin and Tsukuyomi went to check on her.

"Saber!" Shirou cried out. "I'll make sure your reign ends here!" Shirou takes out the Decade watch again.

D-D-D-DECADE!

Shirou inserted the magenta watch into his empty left slot and spun the driver.

ARMOR TIME! KAMEN RIDE! WOW! DECA~DE!

Shirou gains the Decade Armor and summons the armor's respective sword.

RIDEHEISABER!

He starts rotates the weapon's Hand Slecter as Ohma Zi-O brings out the Kuuga Riderwatch.

HEY! KUUGA!

KUUGA!

Shirou creates the energy crest of Kuuga, he then thrust it at Ohma Zi-O.

KUUGA! DUAL TIME BREAK!

As the energy crest heads towards the demon king, Ohma Zi-O stops it with a kick before he summons an energy construct of Lynt Hieroglyphics. He absorbs Shirou's energy crest then does an energy kick sending the construct at Shirou sending him stumbling back.

"An unstoppable will, that is the sign of a king," Ohma Zi-O commented.

"Shut up!" Shirou shouted.

Shirou rotates the Hand Slecter again to Kiva as Ohma Zi-O takes out the Kiva Ridewatch.

HEY, KIVA!

KIVA!

Shirou summons a flock of energy bats charging at Ohma Zi-O which they begin to swarm around him.

KIVA DUAL TIME BREAK!

A ringing noise was heard as the energy bats changed color and headed for Shirou. As the bats left they saw Ohma Zi-O holding the famous Bloody Rose from Kiva's history. The bats start attacking Shirou, making him fall on his knee.

"Shirou… please stop…" Saber grunted.

"She's right Emiya-kun!" Rin for the first time in Shirou's eyes pleaded to him.

"No, I'm not done yet," Shirou grunted.

He rotated the hand one more time and lands on Ryuki while the golden king takes out the Ryuki Riderwatch.

HEY, RYUKI!

RYUKI!

The RideHeisaber is coated with orange flame as Shirou charged at Ohma Zi-O.

DUAL TIME BREAK!

As Shirou was close to his future self and slash him the latter summons Dragreder who arrives to shoot fireballs at Shirou sending him on his back.

"No," Shirou groans.

"If you're that against on becoming demon king…" Ohma Zi-O begins to say. "...Then let me tell you what you can do." Ohma Zi-O looks directly at him. "Get rid of the belt." His words shocked everyone. Was Ohma Zi-O really giving advice to his past self on how to erase him? "If you do that, you won't become me."

Shirou looks at his belt not believing what he was hearing. "Give up… this belt…?" Shirou ran the option on his head. He accepted his belt so his dream and promise to Kitrusugu can happen. Will he be destroying his dream and break that promise. Or was that the only solution to save the future from himself.

AN: I have a lot of ideas for the Fate series, MHA, and Fairy Tail so you'll be seeing a lot but don't worry I got other mangas for one-shots. Someone recommend me Grease Blizzard and Arknight which I only got the henshin down since I have no clue about Arknights, so can someone inform me about the game.