Disclaimer: I don't own Fairy Tail or Kamen Rider and they belong to their respected owners.
Natsu saw the kid reunited with their mother, and seeing that lonely kid made him realize what Primitive Dragon needs. So he ran to where Legeiel was rampaging with Lucy and Happy.
When they arrived, they saw Gajeel and Yuri fighting Legeiel who had gained a new form, Legeiel Forbidden. Legeiel slashed at their chest's creating sparks knocking them to the floor. Legeiel stood sensing the presence he was waiting for.
"There you are, Swordsman of Flame!" Legeiel shouted.
Natsu holds Dragonic Knight Wonder Ride Book as Legeiel sends a small fire twister at Natsu.
"Where there is determination, there is hope!" Natsu exclaimed.
Natsu placed the Ride Book into his Swordriver before pulling his Kaeken from it.
"Henshin!"
REKKA BATTOU!
The large version of Dragonic Knight Wonder Ride Book spawned behind sending out the silver armor at Natsu.
Don't Miss It. DRAGONIC KNIGHT!
Natsu turned into Kamen Rider Saber Dragonic Knight. Saber knocked the twister out of the way before Legeiel charged forward at Saber. They fought and Saber can tell he's not going to make a dent or scratch at Legeiel Forbidden, not with Dragonic Knight.
As Saber was knocked back the Primitive Dragon Wonder Ride Book appeared above him as the Rider's visor glowed blue and the cursed Ride Book replaced Dragonic Knight.
P-RI-MI-TIVE DRAGON~!
Saber let out a dark aura and a feral roar.
"Heh, this is nothing!" Legeiel says as he and Saber charged at each other.
As they fought, both Buster and Saikou got back up.
"You handle Legeiel and I will handle Natsu!" Yuri instructed him.
"Alright!" Gajeel shouted as they went to their targets.
Buster tries to handle Legeiel while Saikou tries to get Saber back to their senses.
Lucy and Happy watch from afar, She and Natsu discover that Primitive Dragon is not just a dragon but a little boy. A little boy who is sad, and somebody that needs to be saved, for him to smile again. Natsu told her and Happy to stay back because he doesn't want to hurt either of them.
Lucy and Happy weren't the only ones who were watching the battle. Gray was watching the battle but he didn't notice Jellal with Ultear and Meredy was watching as well.
Saber slashed at Saikou before kicking the Swordsman of Light back.
"We have to help him!" Ultear says but was stopped by Jellal.
"You would be no help and this is where Saber's transformation will come undone," Jellal explained.
~/~
Inside the mind of Natsu, he was walking through flames of Primitive Dragon, of Haku, and even though he would eat the flames and not be affected by it… these flames were different. The flames of Primitive Dragon looked the same as any other flames but he felt the flames' sorrow, its sadness. It made him want to give up but he can't! He needs to reach out to him.
As Primitive Dragon stopped breathing fire, he looked at Natsu and asked, "Where is everyone? Where are they?"
Before Natsu would punch anybody to knock some sense into them but not this time. He slowly reached to the dragon's skeletal head and hugged it.
~/~
Back in the real world, Saber was about to attack again but stopped mid-way, and torso and head slumped while still standing up surprising everyone.
"How?" Jellal questioned.
"Right now, Natsu is close!" Lucy says. "The answer to saving Primitive Dragon!"
"We'll handle Legeiel till he finds it!" Gajeel shouted before being pushed away by Legeiel.
Legeiel charged forward to strike the immobilized Saber but was blocked by Saikou, Buster joined in trying to give Natsu more time.
Legeiel raised his sword as the blade glowed before stabbing it in front of him creating a wave of rocks at the two Riders making contact and creating a small explosion. The attack made Buster and Saikou de-henshin.
With them out of the way, Legeiel charged back at Saber, the former was about to strike at Saber but his sword was blocked by Blades in King Lion Daisenki's form, surprising Legeiel and the other two swordsmen.
"Gray?!" Gajeel was shocked to see the Ice-mage.
Blades slashed Legeiel backed.
"Natsu may go in without thinking but when it comes to determination, it never leads him astray," Gray says.
Blades began to fend off Legeiel.
~/~
Back inside Saber's mind, Natsu was trying to console Primitive Dragon.
"In the past, dragons and humans lived together in peace." Primitive Dragon told him.
Natsu nodded. "I know, my adoptive father, Igneel told me the story."
Primitive Dragon hummed and continued his story "But one day… humans who were afraid of dragons hunted my friends down till I was the only one left." He explained.
Tears escaped from Natsu as he kept hugging Primitive Dragon as the dragon kept asking where his friends were. His friends were murdered, he was alone but…
"That is not true!" Natsu told him. "Lucy always told me some stories are not over till we know it's truly over. And yours is not over… not yet!"
"Eh?" Primitive Dragon sounded confused.
From what Lucy explained to Natsu, he started to explain the extra lines Lucy wrote to continue Primitive Dragon's story as he wasn't alone, the winds were laughing, the earth had a nostalgic scent, and the fire was warm.
Primitive Dragon changed back to his human boy form, Haku.
"They're all… my friends?" Haku asked.
Natsu got to eye level and gave him a reassuring grin, "Nature is your friend, never forget that!"
"Thank you for finding my friends for me." Haku smiles.
"Why wouldn't I? I'm your friend as well, right?" Natsu says.
"My friend?" Haku tilts his head.
"Yeah!" Natsu held out his hand.
Haku's smile grew wider as he reached for Natsu's hand and held onto it.
A roar was heard and Brave Dragon the spiritual form of Igneel.
"Igneel?" Natsu pondered why he was here.
"Hello, it seems you went beyond my expectations even more," Igneel says, floating above them. "But I'm not here to just congratulate you, but your new bond created a new friend, Elemental Dragon!"
A fiery orange-yellow dragon manifested and floated above them. Haku changed back to Primitive Dragon and floated next to him.
"Elemental Dragon…?" Natsu pondered.
"Yes, back during the age of dragons peace with humans, his name was Belserion, the Sage Dragon. His spirit has returned by the bond you created and want to help you Natsu."
"Follow me, little one!" Elemental Dragon told Primitive Dragon.
"Hai!" Primitive Dragon followed Elemental Dragon up to the air.
~/~
Blades scanned his King Lion Daisenki Wonder Ride Book in his King Lion Booster
KING LION! SPLASH READING!
"Lionic Full Burst!" Blades launch comets of violet-blue energy from his King Lion Cannon.
LIONIC FULL BURST!
Legeiel blocks the blast before sending an electrical slash at Blades making him de-henshin back to Gray. He would have fallen on his back if it wasn't for Gajeel and Yuri catching him.
"Gray-sama are you ok?" Juvia asked worriedly.
"I'm fine but we can't let him get close to Natsu!" Gray exclaimed.
They tried to stop Legeiel but they were all pushed back. Legeiel turned to Saber.
"Disappeared from my sight!" Legeiel sent a fiery slash at Saber.
The slash made contact making a small fiery explosion.
"Natsu!" Everyone cried out.
But their cries stopped when they saw a light blue glow coming from Saber. Looking closely they can see Natsu shaking hands with a little boy.
"He did it?!" Happy cheered.
Lucy smiles knowing Natsu was able to reach out to Primitive Dragon and help him continue his story.
Everyone was surprised to see Natsu held Primitive Dragon's Ride Book and a new Wonder Ride Book.
ELEMENTAL DRAGON!
Natsu opens the Elemental Dragon book.
Joining Hands With The Ancient Power, It Became A Divine Beast Who Could Save Everything.
He then inserts the Ride Book into the Primitive Dragon's Ride Book.
ELEMENTAL DRAGON! GET!
Saber placed the combined Ride Books before pulling Kaenken Rekka out of his Swordriver.
REKKA BATTOU!
Kaenken Rekka's blade was engulfed with fire as the large version of the combined Ride Books appeared behind him.
"Henshin!" Natsu gave a horizontal slash.
BAKI! BOKI! BONE! MERA! MERA! BURN! SHAKE HANDS!
Both Primitive and Elemental Dragon popped out of their respective Wonder Ride Books as they circled around Natsu before connecting their hands together before their hands attached themselves to Saber's chest.
E-LE-MEN-TAL DRAGON~!
Saber had a new look, he wore a red bodysuit except for his legs and arms. He had chest armor that had red and yellow flame designs. On his shoulders were the heads of Primitive Dragon on his right and Elemental Dragon on his left with their conjoined in the center of his chest. Saber this armor pieces from Primitive Dragon like his arms—from his elbows to his hands—and his legs—from his thighs to his feet—along with his robe which was half Elemental and half Primitive Dragon. Saber's faceplate had a more fiery feature with only the bottom X and mouth guard staying powder blue. The blade on his helmet had an orange and yellow edge and a small red center.
Element Mashi Mashi! Kizuna Katame!
Saber had tied the bond with the sad lonely dragon Haku with the spirit of the former Sage Dragon, Belserion combining their power to have Natsu become Kamen Rider Saber Elemental Dragon.
"Heh! It doesn't matter what form you take! I'm invincible!" Legeiel shouted as slash water-styled slash.
Saber moved with great speed with the power of water before doing a water spin attack at Legeiel. Legeiel powered his sword with electricity before throwing at Saber like a javelin, but the latter blocked the attack before rebounding the attack with his own electricity.
"How can this be even possible! Are you even human?!" screamed Legeiel
"Weren't you once human, Legeiel." Natsu contradicts Legeiel.
"Don't be ridiculous! I am…" Legeiel stopped and stared at Saber for a moment as he was remembering something from so long ago. A time where he was happy, kind, and… human.
The Megido shook his head in denial, "That's a lie! A lie! A lie! A lie! A lie! A lie! A lie! I'm not human! I'm a chosen supreme being!" Legeiel screamed in denial.
Legeiel and Saber charged forward and Saber was able to handle Legeiel Forbidden with his Elemental Dragon form. A form that let him use the elemental of fellow swordsman; water, electricity, wind, and earth. When Saber gave Legeiel a fiery slash, the latter began to release some portion of his energy.
"He used the forbidden technique," Yuri explained before saying. "There's no salvation for him. You must save him with your own hands."
Saber stares at Yuri before nodding, Natsu would do anything from killing Legeiel and saving him, but the true Legeiel was human and the human Legeiel died thousand years ago.
Saber inserted Kaenken into his Swordriver.
"I will decide on how your story ends!" Natsu declared.
Saber pressed his fist onto the Elemental Dragon Ride Book.
HISSATSU DOKUHA MASHIMASHI!
Saber pulled Kaenken out of the Driver.
REKKA BATTOU!
"Shinra Banshouzan!" Natsu announced.
ELEMENTAL GASSATSU GEKI!
Saber charges Kaenken with fire before gathering all elements' power and delivering a single rainbow-colored slash to Legeiel.
This pushes Legeiel a few meters away; he was on his knees before standing up. The spirit of human Legeiel, smiling for one last time as his body exploded, ending the former human for good.
As the explosion died down, Saber removes his Ride Books from his Driver.
Elemental Dragon! Thank You!
As Natsu de-henshin, and before he could talk to his fellow guildmates he went back in Wonder World to see Haku, and next to him was a strange-looking man.
"You truly are an amazing person, Natsu Dragneel. Not just a Dragon Slayer but as a swordsman and a hero." The man complimented Natsu.
"Who the hell are you?" Natsu questioned.
"My name is Tassel." He bowed before he turned to Haku. "And I like to thank you for saving this young boy's soul, something no one else could."
"No problem!" Natu grinned. "I'm happy to help and on making a new friend."
"I'm sure she is also pleased," Tassel says.
"She?" Was he talking about Luna?
"Natsu." Tassel's face turning serious. "The world is headed toward the worst possible scenario. You must find her as soon as possible." Tassel explained.
Natsu blinked and he was back in Earthland, 'worst possible scenario'? Is this what Jellal was talking about or is this something else? Before he can think any more his head was tackled by Happy. His friends were coming to congratulate him. Maybe for this second, he cherishes his friends right now.
Gray walked away from the scene with Juvia.
"Gray-sama, do you not want to congratulate Natsu as well?" She asked.
"Not yet. There's still one thing I need to do." Gray says as he walks away with Juvia not that far behind.
With Jellal, he, Ultear, and Meredy watched Fairy Tail members celebrate as well.
"Don't you see, is your prediction still true?" Ultear asked him.
"That future still hasn't changed," Jellal says, only to Ultear and Meredy gave each other worried looks.
~/~
Elsewhere, from afar but close, Storius along with Zeref and Irene Belserion watch the whole scene.
"Legeiel, this is where your story ends," Storius says.
"It seems you knew this would happen," Irene commented.
"The Black Wizard did give Saber the forbidden book." Storius pointed out.
"It was about Haku, the lost little dragon." Zeref explained before leaving the area followed by Storius, while Irene stared at Natsu.
"I knew Haku, he was a sweet boy." Irene frowns. "But that Elemental Dragon… its aura, it felt familiar. Could it have been… Belserion." Irene's frown deepens. "Belserion if that is you, why do you still support humans?" She asked out loud before walking away from the scene as well.
AN: ThunderFlameKnight gave me this idea and I'd put my own twist. I was also kinda inspired by striberx, Fairy Tail Wizard-Tales of Bonds. I wanted it to different with their story as they made the Wonder Ride Books into familiars I decided to keep them in Wonder World and made all the dragons Saber used are spirits from deceased dragons with the Ride Books they're based on. The name Haku came from Ghibli's movie, Spirited Away. For where this take place you can say it's during the beginning of the Alvarez Empire arc.