A week after the day Sin and Yamato met the Whitebeard Pirates, they left Eretzia, leaving Hiyori and Grount behind to focus on their trainings, and their destination was Swallow Island in the North Blue.
Once they crossed the Calm Belt that seprated the New World and the North Blue, it was simply a matter of using the compass to determine the location of the Island, and a journey which was supposed to be completed in weeks, were completed by them in just three hours.
Sin would have arrived here in a matter of minutes if he was alone, but since Yamato was with him, he had to travel at a speed that she could bear and nodded to give her the breaks to catch her breath.
"How are you not tired?" The Oni-Girl asked as soon as they landed on the ground, and she looked like she had been through one of the hardest battles of her life, and it was the truth.
Yamato had been constantly using her Armament Haki to protect herself, and the three hours had been worse on her than the times she had challenged her father and lost to him.
Her head still felt very dizzy, and she was hungrily gasping for oxygen that her body needed, but stragely enough it was not helping her feel better.
"I am Lightning." Sin chuckled at her predicament, and then quickly located the presence of the three people he was there to see.
The three of them were inside Wolf's secret laboratory, and they were seriously working on something, not even speaking much. And when he turned to looked at Yamato again, he sighed in his heart.
He too felt that he had gone a little harsh on her, but he wanted to test her limits. And she had performed well-above his already high expectations.
Deciding not to make it harder on her, he sat down on the snow, and Yamato plopped down as well, closing her eyes to get some rest.
Sin sensed her falling asleep, but he did not disturb her, and used the next few hours to train his Observation Haki, allowing her to get the rest that her body and mind needed.
It took her four hours before she woke up, cutely yawning and stretching her arms, and then she smiled as she saw him do the same.
"Feeling better?"
"Yup!" She happily nodded her head and then took a deep breath, finally paying attention to the snowy land around them. "It's a nice place."
"It is." He smiled. "It's also one of the few Islands in North Blue that is not entirely covered in snow, but it is still very cold here just like any other place in this Sea."
"Have you been to all the places in North Blue?" She curiously asked, and he shook his head.
"Of course, not. There are over three hundred thousand Islands in this Sea, the least number in the Four Blues, and only a few hundred of them are inhabited by people. I have only been to nine Islands here..." He informed her and then started walking towards the hill next to the Pleasure Town where Wolf lived.
Minutes later, Yamato was curiously looking at the entrance of the cave that was hidden in the woods, and then watched Sin knock on the steel door.
They only had to wait for a few seconds before the door opened on its own, and she followed him right inside the cave. The two of them descended the stairs until they arrived in the Laboratory where an old man and two young boys were working on something, wearing their safety goggles.
"Sin!" The boy with the orange hair grinned at him before he rushed over. "It's good to see you again!" He said and then fist bumped with him before curious looking at Yamato.
"It's good to see you too. You have grown quite taller than the last time I saw you." He said and then smiled at Penguin, who was still wearing a hat with his name on it. "I hope you two have not been slacking off in these years."
"We hope you remember your promise!" Penguin grinned at him, and he laughed before he nodded his head and then greeted the old man with sleeked grey hair, who was wearing shorts and a aloha shirt in this cold weather.
"Wolf."
"Sin." The old man smiled at him before he nodded his head, and just like the boys, his attention was soon drawn to Yamato and the horns on her head.
"I am Yamato!" The One-Girl cheerfully informed them, and Sin smiled at her for using her true name this time. "Are you two related?" She curiously asked as she looked at Shachi and Penguin, both of whom were of the same stature, the only exception were their hair, which were orange in Shachi's case and black in Penguin's case, and their noses, which were of different shapes."
"We are Fraternal Twins." Penguin informed her. "Are you strong?" He asked, looking quite excited, and Yamato grinned at him.
"You want to fight?"
"Hey, you kids are not allowed to destroy my lab." The old man spoke up, and then looked at Sin. "Are you here to take the boys with you?"
"That depends on whether their education is complete or not." He said and noticed both the boys confidently grin at his words.
"You can never learn everything about science. Your education continues for the rest of your life if you choose to take this path. However, they are ready." Wolf said, much to the glee of the two boys, and though there was a smile on his face, Sin could sense that the Old Man was starting to feel sad at the prospect of parting ways with Shachi and Penguin.
And it was something he was hoping for.
"I am also here for you, Wolf." He said, making the old man raise his brow at him. "I want you to come with me to Winterheim, and you can continue your Research there. It will be funded by the Crown. Your help will benefit the people of my Kingdom a lot, and Sachi and Penguin can learn more from you for years to come."
He chose his words carefully, knowing well that Wolf no longer had any interest in going on Sea voyages as a Pirate after what happened with his son, and the old man meaningfully looked back into his eyes.
"Law stays at Winterheim now, and once Bepo's current training ends, he will be living there as well."
"How's that Fatty?" Shachi asked, grinning ear to ear.
"He's so strong now that he can kill you with his eyes closed and in just a matter of a l few seconds," He sinisterly replied. "Be at your best behaviour around him."
Penguin gulped at his words, and Shachi nodded to his head too, now a little apprehensive about meeting the Bear Mink again.
However, both the boys knew that Bepo was very kind, and if they behaved themselves, he would never pick a fight with them.
"So, are you coming?" He asked again, looking at Wolf, and both the boys turned to look at their mentor with lots of expectations in their eyes.
"You wouldn't let my old bones rest, would you?" He sighed, and his words were met with cheers by the two boys.
"Of course, not." Sin chuckled, and then they all shared a laugh before Shachi and Penguin left to pack their stuff. "The lunch is on me. You can eat in the town all you want."
Sin told them that he would come back in a few hours, and then he took Yamato with him as he showed her around the Island.
Even the simplest of things made her extremely happy, and having lived most of her life in Onigashima, she even had not gotten a chance to explore Wano. So, every day was now an adventure for her.
Hours later, they met with with Wolf, Shachi, and Penguin at a famous restaurant in the Pleasure Town, and there they had lunch together.
The people of the town were, of course, very alarmed by his presence, and even the Marine Captain of the Island personally came to visit him and welcome him.
It was not going to be long before Yamato, and the three people he was having lunch with were going to ge reported to the Marine Headquarters.
Sin chuckled in his heart as he imagined how relieved Sengoku would be that they had finally found him. He was sure that the Fleet Admiral was going to be very suspicious about his visit to North Blue, and that he was going to take a lot of interest in Yamato. The Marines would be able to gather information on Wolf and the two kids, but not her.
She was not even in the file the Marines had on Kaidou and Beast Pirates.
After Lunch, Sin helped Wolf pack the important stuff that he wanted to take along, as well as the food supplies that they had bought from the town. They put all the stuff in the Submarine that the Old Man had created, which he called his best work to date, and the machine that they were going to take with them.
It was indeed a scientific marvel as it could not just travel underwater, sail on the waters, but could also travel underground, creating tunnels. And Wolf had named it Invincible Hanamaru, which was a funny name, literally meaning Invincible and Excellent Work.
The most excited of them was Yamato, who had never before seen such a machine in her life, and the prospect of travelling underwater and be able to see the aquatic life was like a dream to her.
And it was truly an experience even for Sin once they set out in the sea.
"Where to Captain?" Penguin, who was operating the Submarine, excitedly asked, but his face paled when he heard the Black's words.
"Calm Belt."
"W-what?" Shachi too was shocked, and even Wolf looked a little tensed.
"The Submarine isn't layered with Sea Prism Stone."
"I am aware." He smiled. "Don't worry, the Sea Kings won't bother us." He confidently said.
"Why?" Penguin nervously asked.
"Because I will kill them if they attack us." He harmlessly smiled, and only Yamato grinned at his words. "To the Calm Belt."
"Aye, Captain!" The two kids answered in unison, putting their trust in him, and they headed straight to the New World through the Calm Belt.
And their trust in him proved to be right because when they entered the Calm Belt three days later, not a single Sea King dared to come their way or bother them for the entire eleven hours that they spent crossing it.
Funnily enough, Sin spent all those hours sleeping in his room.