In the middle of the forest, some slayers were training under Tengen's wing.
"Come on, move your bodies! Or do you want to die when the battle begins?" exclaimed Tengen, holding a stick in his hand. Suddenly, behind him, the former Sound Hashira heard a voice.
"I see you're still the same even without a hand, aren't you?"
"Goku-kun, you're finally here! Long time no see, Sun Hashira!" exclaimed Tengen.
"Yup. You look so much better with your hair untied, honestly," said Goku.
"That's why I'm not tying them anymore!" said Tengen. "How long has it been, two months?"
"Yeah, exactly two months," said Goku.
"I heard you fought another Upper Rank. Is that true?" asked Tengen.
"It is," replied Goku.
"Did you lose any limb this time?" asked Tengen.
"No, I risked losing an arm or a leg, but dying? Nah," replied Goku.
"I had no doubt, Goku-kun. Honestly, if you survived against those two Upper Ranks we faced back then in those conditions, I think you've become unkillable," said Tengen.
"Yeah, probably. Now, let's begin the training. I want to get stronger!" exclaimed Goku.
"Fine! Let's go!" exclaimed Tengen.
Shortly after, Goku started to train with the others. He ran faster than anybody, he did more sit-ups than anybody, and most importantly, he wasn't even tired.
(I never thought he had such a muscular physique...) thought Tengen, after he saw Goku without his shirt for the first time. "When did you get so muscular?"
"I trained alone after our mission two months ago," replied Goku, while running in place. "And after the Mugen Train, too."
Shortly after, Goku decided to go for a break. "Hey, Tengen, have you got something to eat?"
"If you're hungry, reach my wives over there..." replied Tengen. Goku nodded, and he slowly reached Tengen's wives.
"Hey, you three!" he shouted. "It's been a long time, hasn't it?"
"Goku-kun!" exclaimed Suma. "It's been so long, it's good to see you're doing well!"
"I can say the same for you. What's that soup there?" he asked.
"Here, have some!" said Makio, handing a bowl of soup to him.
"Thanks, Makio-san!" exclaimed Goku.
"If you don't eat more, I'm going to intensify this training even more!" exclaimed Tengen.
"We'll eat! We'll eat!" said a slayer.
"Always the same, your husband..." sighed Goku.
"Yeah, he hasn't changed a bit since you last saw him," said Hinatsuru.
The next day...
"Let's move on to the next drills! Split into pairs!" said Tengen.
Goku took the closest slayer to him and carried him onto his shoulders. "Hold on tight, I run fast."
At Tengen's signal, Goku sprinted faster than anybody.
"That's not fair, he's a Hashira..." said a slayer.
"Stop complaining and run faster!" said Tengen, hitting the slayer with his stick, making him run faster.
Later on, when Goku was doing push-ups, he heard the voice of a slayer.
"Why would a Hashira train with us newbies?" he asked.
"Because I want to get stronger," replied Goku, doing a push-up.
"Couldn't you train on your own?" asked another Hashira.
"Nope," Goku explained, sitting up. "I could, but it wouldn't be as efficient as this one."
"Tsugikuni-san, we've heard you faced three Lower Moons and three Upper Moons. Is that true?" asked the slayer.
"Yessir. I faced Lower Moon Four, Five, and One," explained Goku. "Then I faced Upper Three, Upper Six, and Upper Four. Even if the Upper Six were two, actually..."
"You really are crazy strong, Tsugikuni-san..." said a slayer.
"Yes, but not enough," said Goku. "Not enough to defeat Muzan or the last three Upper Moons remaining..."
"Tsugikuni-san, how does fighting an Upper Rank feel?" asked the second slayer. "And what about the Mark?"
"Well, as for the Upper Ranks, I'm not ashamed to say I was about to die every single time. Except when I faced Lower Moon Four," explained Goku. "I was injured, but not badly. As for the mark, I first awakened it in my battle against Upper Rank Six, though I was born with it. It's strange, isn't it? Being born with a mark and not being able to use it..."
"How did you lose your right eye, Tsugikuni-san?" asked the first slayer.
"Against Upper Ranks Six," Goku replied. "Tengen was with me; he can confirm."
"I confirm!" shouted Tengen from afar.
The next day...
"Today, you're hitting that mountain!" exclaimed Tengen. "Take a lap around its foot and return!"
"Nothing easier!" exclaimed Goku, already starting to run towards the mountain.
(He really is my brother in arms...) thought Tengen, smiling.
(Everyone here has the potential to become a Hashira...) thought Goku. (But, to think about it, Muzan is the progenitor of all demons. So, technically, if we really defeat him, all demons on Earth will disappear... So, what would the Demon Slayer Corps be good for at that point?)
At night, Goku remained with Tengen's wives, helping them clean out the dishes.
"You're so kind, Goku-kun, to help us without asking for!" exclaimed Suma.
"Don't worry, I would do everything to help my bro," said Goku. "And also, I consider this a training too!"
(And also because Tanjiro-kun would have done it too...)
"Drink this, Goku-kun, it's a high-quality gyokuro tea!" exclaimed Hinatsuru, handing a little cup of tea to Goku.
"Thanks, Hinatsuru-san!" exclaimed Goku, drinking the tea.
"Goku-kun, we want to thank you again for what you did at the Entertainment District," said Makio.
"Huh, it wasn't just me... There were Tanjiro-kun, Inosuke-kun, Zenitsu-kun, Nezuko-chan, and Tengen with me," said Goku. "Even if I eventually killed both demons, that's not one-hundred percent my merit..."
"Yeah, we know, but you've been the best," said Suma. "And the truth is, Tengen-dono still wants to fight. I hear him blaming himself for leaving the Corps in the sleep..."
"Goku-kun, please, defeat Muzan Kibutsuji, okay?" asked Makio.
"I will, I promise!" said Goku, resolved. (Everyone's counting on me, I can't fail them! I know, I won't be alone when the final battle begins, but I'll be one of the strongest out there, if not the strongest, depending on how my training goes...)
Chapter 44 - End