Several days after Goku's meeting with Shinobu, the boy kept training, though he had to do it alone, since Rengoku was outside, on a mission. In the night, when everyone was asleep, Goku trained his Sun Breathing. Not because he wanted to show it to them someday, but because he had to know how to use it in moments of need.
One day, when the sun was shining in the sky, Goku was training his Flame Breathing in the courtyard.
"Flame Breathing: Fifth Form -- Fire Tiger!" he exclaimed, executing the form, "compared to the first day I arrived here, I've grown much stronger... I think I can even rival the strongest Lower Moon now..."
He looked at his hands.
Suddenly, from behind, Goku heard a voice.
"BOOOOOOSSS!"
It was Inosuke.
"Inosuke-kun!" exclaimed Goku, with a smile.
"Guess who's back, boss! We've got our swords back!" said Inosuke.
"Oh, that's fine! So now you can fight again?" demanded Goku.
"Yes, we can," said another voice. Goku turned and saw Zenitsu.
"Zenitsu-kun!"
"We've been totally rehabilitated, we're ready for the possible mission. Even if, I'm still afraid..." mumbled Zenitsu.
"I understand," said Goku, "where's Tanjiro-kun?"
"Here!" Goku turned back and saw Tanjiro behind him.
"Tanjiro-kun! Is your arm okay?" he asked.
"Yes, but... it is still broken," replied Tanjiro, "I have to wait a little more before fighting again. Unfortunately, I fear I can't join you in the next mission..."
"No problem, Tanjiro-kun," said Goku, smiling. For the rest of the day, Goku just relaxed, as his training was already complete.
In the night, Goku adjusted his stuff inside his room.
"Time to sleep, I guess..." he muttered under his breath, lying down the bed. But then, just when Goku closed his eyes, he heard kncoking at his door.
"Come inside, whoever you are," he said. Suddenly, when the door opened, Goku saw Inosuke jumping on him.
"HEY, BOSS!" he shouted.
"WOAH!" yelled Goku, rolling aside to avoid Inosuke's jump. Then, he also saw Zenitsu and Tanjiro coming inside.
"Can we sleep here for tonight?" asked Tanjiro.
"Why?" asked Goku.
"To celebrate our first day after the rehabilitation!" answered Tanjiro, "we're friends, right?"
"Fine," said Goku, sighing, "you can all sleep here"
"Thanks, Goku" thanked Zenitsu. And so, that day, without even knowing why, by the end of the night, Goku's room became an apartment for his three friend.
Tanjiro was the only one who was sleeping in a proper position. His broken arm didn't allow him to move freely. Zenitsu was sleeping upside down. As for Inosuke, his sleeping position couldn't even be explained. Goku, who woke up earlier than everyone, seeing their friends sleeping, sighed.
"They are a bit invasive..." he said, "but I care about them, very much..."
Suddenly, Tanjiro's box opened. Nezuko showed up and slowly crawled towards Goku.
"Mh?" she said.
"What is it, Nezuko-chan?" asked Goku. Suddenly, without saying nothing, Nezuko took Goku's hand and placed it on her own head.
"Oh, so you like headpats..." realized Goku.
Nezuko nodded in confirm.
"Fine..." mumbled Goku, "Nezuko-chan... Why are you so attached to me? We barely saw each other, so why are you so affective towards me?"
Nezuko shrugged.
"Oh, right, you cannot talk..." remembered Goku, "maybe... I know why you're so attached to me... since you cannot talk, I think you won't tell anybody."
"we're both demons, Nezuko. I'm a hybrid, to be honest, but it's for this reason we understand each other, I think. We both are good demons, but nobody knows my true identity..."
Nezuko tilted her head on the left side and made a soft "Mh?", signaling she was confused.
"I know, it's hard to understand, but... Everything's true," said Goku, "I'm half demon. Don't tell anybody, Nezuko-chan. Not that you can, even if you wanted to..."
Nezuko stayed still for a moment, looking right into Goku's eyes. Then, she smiled and made a "Mh!"
Goku smiled back and caressed her head.
"Tanjiro-kun is lucky, Nezuko-chan..." he sighed, "I would also really like a sister..."
Suddenly, the door opened again. This time, it was Rin.
"Caw! New mission, all of you aside from Tanjiro Kamado! New mission on the Mugen Train! Caw!"
"Okay, okay, wakarimashita, Rin!" said Goku.
The boy shook Inosuke's, Zenitsu's, and Tanjiro's bodies.
"Hey, you three, woke up, we have a mission!"
"Uhm... What is it, Goku...?" asked Zenitsu.
"We have a mission. Me you, and Inosuke-kun," explained Goku, "hurry up, Zenitsu-kun."
"Goku, I want to come with you..." said Tanjiro.
"With that broken arm of yours? Forget about it," said Goku, "I'm saying it for your sake, Tanjiro-kun."
Suddenly, the boy felt himself pulled by the light-blue haori. When he turned, Goku saw Nezuko, who looked at him as if to say, "can I come with you?"
Goku tilted his head.
"You want to come with us?" he asked.
Nezuko nodded.
"I understand," said Goku, "get in the box. Sorry, Tanjiro-kun, but I'm taking your sister with me for this mission."
He placed a hand on Tanjiro's shoulder.
"I swear on my life, nothing bad will happen to her."
"Arigatou, Goku," said Tanjiro, smiling.
"No problem," said Goku, "now we should go. Even if it's early morning, the Mugen Train is far from here, it'll take until moonlight to arrive there."
Zenitsu and Inosuke both nodded. Then, Goku carried Nezuko's box on his shoulder and grabbed his katana.
"See you soon, Tanjiro-kun. I promise you we'll all come back alive," said Goku, before closing the door, leaving Tanjiro alone, inside Goku's room.
"Be careful, Goku..." whispered Tanjiro.
Later, that day, the trio -- Goku, Zenitsu and Inosuke -- arrived in front of the Mugen Train.
"WOAH!" exclaimed Inosuke, "it's the conqueror of this lands!"
"No, it's a train," said Goku, "have you ever seen a train?"
Inosuke, in answer, took a few steps back, then snorted and charged at the train. The boar heatbutted the train.
"YOU'RE TOTALLY OUT OF MIND, INOSUKE-KUN!" yelled Goku, pulling Inosuke aside and running away.
"Why are we running away, boss?" asked Inosuke, while his back crawled on the dirt.
"Because here, us demon slayer are not allowed!" explained Goku, "so hide your swords, you two!"
As the three of them hid, Goku dropped Inosuke down.
"Don't catch the eye anymore, please," he said, "I'm tired of running."
"Understood, boss!" exclaimed Inosuke, thumbing up. Suddenly, Goku heard a sound. When he turned, he realized: The train was starting.
"Hey! Hurry up! The train is about to start!" exclaimed Goku, alrady running towards the train and gripping on it at the last second.
"Help me, boss!" exclaimed Inosuke, prolonging a hand to Goku, who helped him to get on the train.
"Help meee!" screamed Zenitsu, who was running after the train.
"Take my hand, Zenitsu-kun!" said Goku. Without hesitating, Zenitsu grabbed Goku's hand and finally got on the train. Then, Goku heard Nezuko's box moving.
(She's awake, it seems...) he thought.
"Are you sure it's safe to take Nezuko-chan with us?" asked Zenitsu.
"Yes," said Goku, "she asked me to come, and I promised Tanjiro to protect her. She'll help us."
Then, the three friends took a look at the night sky.
(A new adventure is about to begin...) thought Goku. And indeed, he was right -- A new adventure was about to begin.
Chapter 13 - End.