I don't own Black Clover or Kamen Rider and they belong to their respected owners.
Asta was de-henshin but was being careful and with the help of Noelle and Nero helped from letting the Megid get their hands on the forbidden tome.
The forbidden tome glowed before opening, making Asta look at a specific page it was open to. The text glowed making Asta look away as he read the ancient text.
The skeletal claw popped out of the forbidden book knocking Legeiel away before wrapping itself around Asta.
"Asta!" Noelle cried out.
Nero stared at it with a surprised look, the skeletal claw knocked but why didn't it push Asta away unless…
"Rahhh!" Asta screamed as the claw released its power onto him.
The forbidden tome glowed before turning into dark purplish smoke and turning it into a Wonder Ride Book, called Primitive Dragon.
PRIMITIVE DRAGON!
"Asta!" Noelle tried to get his attention while Nero was still surprised at this forbidden tome turning it into a Wonder Ride Book and by a look at it and Asta she's having a bad feeling about it.
Asta was breathing heavily before finally calming down and looked up at Megid with his eyes turning slightly purple before going back to green.
Asta, straighten up before opening his new Ride Book to its Story Page.
PRIMITIVE DRAGON!
The Wonder Ride Book, as it let out a creepy crunchy tone. Asta then placed Brave Dragon Ride Book into Primitive Dragon's Story Page
BRAVE DRAGON! GET!
Asta then inserted the Ride Book into his Seiken Swordriver and held on to his sword handle. A large version of Primitive Dragon and with Brave Dragon in it appeared behind him with a skeletal dragon on top of it.
"Is that a dragon…" Noelle commented more than asking.
"Yes," Nero affirmed. "But it's more different than Asta and Calibur dragons."
"But the power is similar to the devil but somehow different," Noelle says. "Now I know why the grimoire was locked away but did it create a new Wonder Ride Book for Asta?"
Nero may be old and learn many things from the first Magic King but she has never seen this before.
Asta cranks his neck looking at Megid with emotionless eyes before saying,
"Henshin." He pulls out Kaenken Rekka from his Swordriver making the Primitive Dragon close on Brave Dragon and the larger version coping it.
REKKA BATOU! HAKI! BOKI! BON!
Asta was then engulfed by red flames as the skeletal dragon floated above him showering him with cyan and violet energy before hugging him and creating his new armor
GAKI! GOKI! BON! PRIMITIVE~
Asta's Saber Form was different from any of his others. His full black bodysuit, the armor stands out in a creepy way as the armor looks like dragon bones. On his left shoulder was a skull of a dragon that had two small bones under it which lead to the bone claw on his chest. What's surprising is that the Brave Dragon Ride Book formed on his left side of his body is covered with the bone claw mimicking how it's similar to the Primitive Dragon Ride Book that was covering Brave Dragon Ride Book in his Driver. His arms, hands, legs, feet, and even his tunic had the blue shade bone markings. He became Kamen Rider Saber Primitive Dragon
DRAGON!
Saber let out a shriek before releasing energy making anybody around him step back. The members stepped back with hesitation on the energy he just released.
Saber held his sword in an unknightly way, he growled and crouched like an animal ready to attack its prey.
"Just what the hell is that supposed to mean!" Legeiel responds to Saber's growls and charges forward.
Legeiel was going to strike Saber but was stopped when the latter grabbed Megid by the collar and started pushing him back.
Saber growled and charged at Legeiel and attacked him. Saber's movements were abnormal. It was like the Rider's movement became animalistic. But it was working as Legeiel couldn't get a single hit on Saber with how the latter kept hitting him.
Legeiel jabs his sword forward but the sword is caught by Saber as the Magic Knight pulls the monster over and starts slashing at him before knocking Legeiel to his back. Saber let out a disturbing growl as he jumped and sword aiming for Legeiel who rolled away in the last second. Saber held his sword by the blade as slowing walks towards Legeiel.
Storious ran to Legeiel's side as the latter got back up.
"Legeiel, he's more dangerous than you think," Storious told his comrade and let out a powerful slash at Saber hitting the Rider but had no effect.
Saber attacked the Megid as the monsters tried to defend themselves from Saber but to no avail. Saber was too strong and quick. They tried to strike him but he always dodged or blocked their attacks and only to get slash by him.
"What the hell is this?!" Legeiel sounded frustrated. "Is this really the same Swordsman of Flames?"
Storious was on the ground and having Saber punch him like an animal tried to beat its opponent to death.
The other Riders arrived to see Saber's new form and wild attacks.
"What-" Luck looked shocked.
"Is that Asta?" Yuno asked.
"You guys!" Noelle got their attention as she and Nero ran to their sides.
"Noelle, what happened?" Luck asked.
"The Megid were in Southern Logos Base and stole this forbidden grimoire which someone gave Asta this new Wonder Ride Book," Nero answered.
"Then he started going crazy with this new dark power!" Noelle added.
"It's because he's gone berserk. He's not in control." Lemiel says.
"Berserk?" Blades looked at the berserk Saber.
"What do you mean by that?" Nero asked Saikou, who didn't respond and kept watching the berserk Saber.
Saber let out a ferocious growl before putting Kaeken Rekka back inside the Swordriver and pressed on his now open Ride Book.
GRAPPU HISSATSU DOKUHA!
Saber was engulfed with energy getting ready for his finisher.
"This is bad we must retreat!" Storious told Legeiel.
"You think me that weak?!" Legeiel shouted back. "I can overwhelm him easily!"
Legeiel let out a powerful slash creating rock, ice, and fire projectiles at Saber.
Saber pulled out Kaeken Rekka.
REKKA BATOU!
Saber had purple energy around him as a bone claw came out of the Wonder Ride Book destroying the projectiles before it grabbed Legeiel.
CRASH HISSATSU GIRI!
The claw pulled Legeiel towards as Saber gave a violently powerful slash at the Megid covered in powder blue and black energy. The slash caused a deadly shockwave making Noelle create a water shield in front of them but it was no use as it blew everyone back upon impact and made the other Riders de-henshin.
"Wh-what immense power…!" Yuno says as he felt the pain from the explosion.
Saber stands there before he too de-henshin. Asta's face was covered in sweat and breathing heavily before he finally fainted after the use of that great power of Primitive Dragon.
AN: I had this ready after Primitive Dragon came out but now I finally am able to release it. Also, just watch Zenkaiger and I love it, makes me want to create EP. 1 one-shot. Also, if you read the end then I made the cast into Saber Riders, and here's who is who; Asta as Saber, Yuno is Blades, Yami is Buster, Luck is Kenzan, Magnu is Slash, Lemiel is Saikou and for Espada and Calibur are still the same as the show… it's a work in progress.
Also, my previous one-shot where I had put Touma and not Shouto, has been fixed, I get into the episode I'm not realizing I'm not putting Shouto's name but Touma, so thanks to the reviewers for pointing that out.