Shichiseiken

"Hahahaha…You'll make a fine sacrifice, I'll let Shichiseiken drink you blood!" Saga declared with a wicked grin as he tightened the grip on his sword.

SWOOOSH!! In an instant, he managed to close the distance between him and Kai before he delivered a powerful horizontal slash aimed at Kai's neck. Kai obviously felt the killing intent from Saga using his Observation Haki and used it to predict his attacks.

In a swift move he crouched, avoiding the blade by a few inches. He then launched himself up while throwing a strong left uppercut, that sent Saga flying upwards before crashing down to the ground. 

"A-AGGHH!!...You fool, I'll make you pay for this!" Saga groaned in pain. He slowly rose up while flashing a hostile look at Kai, his pride was certainly hurt after being knocked down that easily. As the sword's control increases over him, it's making him madder and crueler than he originally is.

For Kai, he could've ended the fight way earlier if he wanted to, but he was interested to see what the cursed blade was capable of.

Saga frowned as he thrusted his sword with a strong force, generating green flames and hurling them as a large explosive fireball in a ranged attack "Mystic Fireball!!"

"Cloud Wall" Seeing that, Kai proceeded to generate clouds from his arm while making them very dense before he created a tough barrier of clouds in front of him.

BAAAAM!! Saga's green flames hit the cloud wall, creating a large explosion.

"What an interesting power that sword holds…" Kai remarked, his eyes locked on the beautiful sword emitting radiant green aura "…I'll be taking it from you" 

"You think I'm gonna give it up that easily?! With the help of this sword, I'm gonna be able to achieve what I couldn't even dream of!" Saga yelled madly as he started attacking Kai relentlessly. 

FWOOSH! FWOOOSH! 

"Mystic Snake…Fang Attack!!" With a mighty thrust, Saga generated a blue flame snake and attacked Kai with it, in which the snake tried to bite him. Kai effortlessly tilted his body to the side before he punched Saga to the face, sending him hurtling backwards before he threw a mouthful of blood. 

"COUGH-COUGH!!..." 

With each hit Saga grew madder. Seeing the overwhelming difference between him and the young pirate standing in front of him, he decided to go all out. 

Saga proceeded to lunge at Kai, swinging his sword diagonally and unleashing a powerful flying green flame slash.

"Mystic Fire Slash!!"

BAAM!! Kai quickly took out his hammer and redirected the slash away, causing it to shatter a wall. 

"I think I've seen enough, time to end this fight" Kai declared while slowly approaching Saga. The latter's veins bulged in anger upon hearing that declaration and he didn't waste any time and began attacking Kai again. 

This time he channeled all of his power into his strikes, generating powerful shockwaves with each swing from his sword.

SWOOOSH! With blinding speed Kai dashed at Saga after channeling lightning into his hammer.

"…?!!" Saga was shocked at that speed and couldn't react at all.

"Mjölnir Thunderclap!!" 

Lightning! Thunder! While gripping Mjölnir with both hands he proceeded to swing it horizontally, smashing Saga's face and sending him flying back unconscious.

"…" Saga's men grasped in shock after witnessing that scene, they never imagined that their master would get defeated that easily and they knew better than to mess with the one who defeated him, so they just went to check on Saga and let Kai and the crew do whatever they please.

"Why did you take that long to defeat him?!" Kid appeared from the back, wrapping his arm around his brother's neck before squeezing it "You made my blood boil!" 

"Alright, alright I understand, now let go!..hmm?" Kai noticed Shichiseiken lying on the ground and approached it with intrigue "I like this sword. I think I'll keep it" he said. He decided that he will keep it for himself for now until he decides if it might be better to just give it to someone else. 

"You sure you wanna do that? You might end up being under its control like that guy" Bonney warned him one more time about the risks.

"How can I call myself the future pirate king, if can't even tame a sword" Kai gazed down at the sword for a moment before he reached out for it and grabbed it from the hilt. Everyone waited in anticipation to see what's gonna happen. 

The second Kai made contact with the sword he felt a strange energy jolting his body, it is though the sword spirit was trying to take over his mind and body and the weapon started emanating radiant green aura. It reminded him of Enma and how it tried to drain all of Zoro's Haki until he managed to tame it.

Kai's eyes flashed red as he lost control for a second, swinging Shichiseiken with immense force and unleashing strong green flames in the form of a flying slash.

FWOOOSH!! BAAAM!! The attack accidentally flew towards his crew, luckily, they were able to dodge it before they were hit. 

"Hoi, hoi! Are you trying to kill us?!" Kid exclaimed in surprise before glancing at his brother who appears to have an inner battle as his whole body was shaking and sweating heavily.

"Don't tell me he lost control?!" Bonney remarked, her forehead was drenched with cold sweat from the thought of that.

Kai was struggling to control his actions and thoughts. He proceeded to tighten the grip on the sword until his arm veins bulged while trying to push out all the energy off his body.

"Don't you even dare!!--*Lightning*-*Lightning*" Kai shouted at the sword while unconsciously releasing a strong burst of Conqueror's Haki that rendered all the marines nearby unconscious and even accidentally forced some of his crewmembers down on their knees. Kai was trying to assert his dominances over the sword, and he succeeded for the moment as Shichiseiken stopped trying to seize his mind "Phew!" 

"Haoshoku Haki, you did it again" Kid wore an excited grin after witnessing that. He was already familiar with Haki and it's three types as Kai made sure to explain the basic forms to him.

"I felt a tingling sensation through my body" Krieg muttered while looking at his hands.

Kai raised the sword in the air, admiring its appearance before he walked to one of the unconscious marines and took a sword sheath from him and wore it on the left side of his belt, and then sheathed Shichiseiken afterwards.

So now he has his hammer Mjölnir hanging in the right side while Shichiseiken on the left.

A few minutes was passed since Saga was defeated by Kai before Maya finally made an appearance. After she arrived at the dojo and look at the scene, shock was evident on her facial expressions.

The scene of countless marines lying on the ground along with her husband was something she didn't anticipate. Even though she knew the Kai and the crew were strong but still had a little faith in them to defeat Saga. 

But what made her more shocked was the fact that Kai was now carrying Shichiseiken instead. She watched him in horror before she muttered "Y-You…You used the sword?!" 

"Don't worry, I'm not that weak to be consumed by a mere sword. And since I'm the new owner your husband should be able to break free from its influence" Kai stated, prompting Maya to glance behind him, only to see Saga on the floor and covered in blood and injuries

"--Saga!!"

"--Saga!!" She immediately rushed towards her husband and began treating his injuries, she expected people to get hurt after all, so she came ready.

While she was gently applying bandages Saga slowly opened his eyes.

"…Maya" he mumbled, smiling warmly. When Maya saw that, tears started pouring down her cheeks and proceeded to hug him.

"Welcome back"

After witnessing that scene, Kai turned on his heels and walked away but before he could exit the dojo Saga called him from behind.

"Thank you!"

Kai frowned when he heard that "Don't be, I never planned to save you. In fact I wouldn't have hesitated to kill you if it meant getting my hands on this sword" 

"Still, thank you…I feel embarrassed about this whole thing" Saga said, lowering his head "…. I bet Zoro would be disappointed" he said to himself under his breath while looking disheartened. 

Kai managed to catch Zoro's name "Zoro?" he questioned, interested to know this man's relationship with him.

"You know him?"

"Well, kind of" Kai responded.

"Isn't he that famous Pirate Hunter from East Blue?" Kid stated, even though it might not look like it something he would do, but Kid started to make sure to read newspapers and stay up to date with the world information. 

It was particularly after what happened with Mihawk because he couldn't recognize him as the 'Strongest Swordsman in the World' and recklessly attacked him.

"We're childhood friends, we used to train in the same dojo when we were younger. We even made a promise to each other…"

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Three Years Earlier…A town somewhere in East Blue,

In an empty alley somewhere near the town's port, a green haired figure with three swords was surrounded by several pirates. They were armed, with their weapons drawn and poised to fight. 

Without a notice they all lunged at him at once, aiming to kill him.

The figure quickly unsheathed his three swords and proceeded to cut them down with ease.

FWOOSH!! SPLASH!!

"--AGHHH!!"

"…" 

"You're Roronoa Zoro, the Pirate Hunter!!" Exclaimed the captain of the pirates, he was standing a few meters away from him. He looked panicked after witnessing his crew getting defeated very easily. 

Zoro calmly put back his swords into their sheath "I heard you're the strongest pirate in these seas. I guess it was just a stupid rumor" he said in disappointment, before turning back and slowly walking away. 

"We're not finished yet!" The pirate captain quickly pulled two guns and aimed them at Zoro, trying to shoot him from behind.

"Hmph…Those guns aren't going to work on a man like him" A confident voice spoke, picking the attention of both Zoro and the pirate captain.

"What?! Who the heck are you?!" The pirate captain quickly glanced to the side, trying to identify the person who spoke. It was none other than Saga.

The pirate swiftly turned to the side, aiming his guns at Saga instead but before he could fire any bullets, the swordsman already charged at him with his katana drawn and with a simple strike he managed disarmed him before knocking him out with one punch in the face. 

Saga turned his attention to Zoro afterwards "Long time no see"

"Saga, is that you?" Zoro's expressions softened a little when he saw him.

"I also started a journey to work on my skills as a swordsman" Saga stated while approaching Zoro with a smile "I knew we'd run into each other again, Zoro" 

Zoro noticed the short sword hanging from Saga's belt, it has a brown hilt and sheath and has Zoro's name etched into the hilt "You still have it" he said.

"Of course. It's the dagger you gave me for our promise" Saga responded. Zoro gazed at it in silence "You haven't forgotten, have you? We made a promise on the morning you left the dojo!...You're going to become the world's greatest swordsman, and I'm going to become the sword of justice!"

Zoro cracked a smile hearing that "How can I forget?"

Saga smiled back in relief "You joker! Hahahaha!"

After their fateful encounter the two of them started working together to fight pirates. Together, they managed to take down countless pirate crews until one incident changed everything.

A few months later,

Somewhere on the sea…On board of a medium sized vessel,

While roaming the sea, a pirate crew raided the ship that Zoro and Saga were boarding.

"Get them!!"

"Kill them all!!"

"What morons! Who do you think is on this ship?!" Saga exclaimed confidently while effortlessly cutting down pirates, Zoro was also fighting alongside him.

For a moment everything seemed to be going to their advantage until an unfortunate incident happened, while Saga was fighting, a large wave hit the pirate ship beside them prompting the anchor chain to fly towards his direction. 

He only noticed late and got trapped by it. Now his right arm trapped by the chain while he is hanging down from the massive hole at the center of the ship's deck that was caused by the anchor, Saga struggle to free himself.

"Aagghhh!...Damn it!"

"Saga!" Zoro quickly finished off his enemies and hurried to his friend's rescue.

"The gunpowder!" To make the situation worse a fire was ignited near the gunpowder barrels stored on the lower deck.

"Saga!"

"Zoro!" 

"I'll take care of it!" Zoro said as he tried to break the chain with his swords.

"You can't--Damn it!..." Saga was in intense pain "Zoro, there was an axe in the captain's room! Go get it, we need it!"

"Don't be stupid, I'm not gonna leave you here!"

"I'll be fine, hurry up and go, Zoro"

"I'll be right back, just hang in there! I'll definitely get you out of here, I promise!"

"Yeah, I trust you. Don't screw it up, Zoro" Even though Saga said those words, it seems that he had a little faith in his survival from this situation. 

BOOOOOM!!! 

Unfortunately, the second Zoro turned his back on Saga, the gunpowder exploded and propelled him out of the ship. 

"Saga!"

"SAGA!!"

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"…I miraculously survived the explosion but lost the use of my right arm" Saga said while clenching his right arm tightly "I fell into a state of depression and only because of Maya that I got better…That until I found Shichiseiken, I can't believe you're carrying it around without being affected by it"

"Skill issue"

"Hahaha, I guess it's true…But there is something I realized after all these years, it doesn't matter what kind of justice you believe in. It's all useless if you don't have power…" 

"…because whoever has power, decides what justice is"