Goku arrived just in time to save Tanjiro and Nezuko from near death. After his arrival, the two brothers hid, and Goku remained alone against Rui.
"So... You said you defeated Mukago, didn't you?" Asked Rui.
"That's exactly what I said, Rui," replied Goku.
"So, because Mukago was stronger than me, now you think that you can beat me as well, is that right?"
"That's precisely right."
"Fine," snorted Rui, injecting his spiderwebs with blood, "then I'll enjoy even more breaking you into a million pieces."
"Blood Demon Art: Cutting Thread Cage," said the Lower Moon, caging Goku inside his red spiderwebs.
"I already neutralized this attack once," said Goku, "how can you think it'll work this time?"
"Flame Breathing: Second Form -- Rising Scorching Sun!" He exclaimed, and the spiderwebs got cut off.
(It didn't work... this guy really is strong...) thought Rui, (and why does he smell like sun..?)
"First Form -- Unknowing Fire!" Exclaimed Goku again, dashing forth into Rui's direction.
"You won't cut my head off!" Exclaimed Rui, generating other spiderwebs and throwing them at Goku.
(Shit... I have to interrupt the attack, if I want to dodge...) thought Goku, (or maybe... I can tank the attack and counter with an attack three times stronger!)
Goku didn't interrupt the Breathing, slashed through the spiderwebs, though some of them cut his legs and arms. But now, Goku stood in front of Rui, ready to cut his head.
(No... He managed to close the distance...) realized Rui. But suddenly, when Goku least expected it, he got trapped inside a web cocoon.
The boy found himself closed in and with no escape points. Rui's sister, who had been watching all the time, showed up.
"Did I tell you to intervene?" Said Rui, who seemed to everything but grateful.
"But you... you were about to be defeated, Rui..." she said.
"Shut up! I wasn't!" Yelled Rui. Meanwhile, inside the cocoon, Goku tried to cut the webs.
(I can't cut through... What will this cocoon do to me...?) He wondered.
"Free him," said Rui, from outside. "I want to kill him by myself."
"Are you sure, Rui?" Asked the sister.
"I am," said Rui.
Suddenly, the cocoon exploded. Goku jumped high, his blade wrapped in flames.
"No need to free me! I freed myself alone!" He said, his silhouette enlightened by the moonlight, "Flame Breathing: Fifth Form -- Fire Tiger!"
Goku, still in the air, threw at Rui, behind him, appeared a tiger-like flame. Rui's sister ran away in fear, and Rui got overwhelmed by the fire tiger.
(What... What's happening...?) wondered Rui. In the blink of an eye, Goku reappeared in front of him.
"Second Form -- Rising Scorching Sun!" Screamed the boy. His blade collided with Rui's neck, and after an incredible effort, Rui's head shot up.
(I... I did it... I beheaded him...) thought Goku. Then, due to the incredible effort -- both of the Flame Breathing and physical force to behead Rui -- Goku fell on his knees.
From a tree nearby, but safe, Tanjiro kept watching the fight, still holding Nezuko in his arms.
(Goku-san really won...) He thought, (he's really incredible...)
Slowly, Goku got to his feet, panting heavily and clutching his chest.
"Tanjiro-kun, where are you?" He asked loudly.
"Here, Goku-san!" Answered Tanjiro, showing up.
"Let's go, we must save the other two demon slayers who were with you!"
But suddenly, some spiderwebs appeared and tried to hit Goku.
"Goku-san!" screamed Tanjiro. Without hesitating, Tanjiro dropped Nezuko and ran to Goku.
"Tanjiro-kun, what are you doing!?!?" Asked Goku. But before he could finish the phrase, Tanjiro was already in front of him. The spiderwebs hit Tanjiro, slicing through his body. In that moment, Goku heard a strange sound, like a bone breaking.
Tanjiro spat blood and crumbled to the floor. There, Goku realized: Tanjiro's left arm broke.
"G-Goku-san..." whispered Tanjiro, "my... my arm, is broken... the demon's still alive..."
"But... How?" Wondered Goku, "I beheaeded him..."
Suddenly, Rui's body rose on his feet, and Rui's head appeared from a tree, held in mid-air by a rope.
"You really thought you had killed me? I managed to slice my own head with a spiderweb before you could do it with your sword," he explained.
(Goddamn... He's still alive... And Tanjiro is practically unable to move... I have to fight...) realized Goku. Then, the boy turned and saw Nezuko. She had a worried expression on her face.
"Mh?" She made her usual sound.
"Your brother is fine, don't worry..." said Goku. Meanwhile, Rui's head returned attached to his body.
"So, shall we begin with Round two?" He asked.
"I'm ready...!" said Goku. However, suddenly, another guy arrived. But this time, it was on Goku's side.
Instinctively, Goku took Tanjiro, barely conscious, and brought him away.
"Who's this guy...?" Muttered Goku. The guy had long black hair and a mispatched haori.
"You've fought well, slayers," said the guy, "it's a good thing you're not dead."
"Who... Who are you?" Asked Goku.
"Giyuu Tomioka," answered the guy, already looking at Rui, "the Water Hashira."
"I... I know this guy..." whispered Tanjiro, "I met him two years ago, when my sister became a demon..."
Then, Tanjiro definitely fainted.
"Another slayer? No problem... I'm gonna kill you first..." said Rui. But like it ain't nothing, Giyuu drew his sword and said this:
"Water Breathing: Eleventh Form -- Dead Calm."
In the blink of an eye, Rui's Blood Demon Art was neutralized, and before the demon could even notice, Giyuu beheaded him.
(This guy is a tough one...) thought Goku. As Rui's head dissipated into nothingness, the boy stared at Tanjiro's fainted body.
"H-Hey, Tomioka-san!" He exclaimed, "Can you do something for him?"
Giyuu slowly turned to face Goku and recognized Tanjiro and Nezuko.
"I... already met them," he said, "and unfortunately, I can't do anything to heal him."
"He has a broken arm..." said Goku, "help him, please!"
"Maybe... The girl who came with me can heal him..." hypothesized Giyuu, "even though I think both him and his sister are under arrest. A demon slayer can't carry a demon with them."
"But she's his younger sister, he has to!" Said Goku, in Tanjiro's defence.
"Don't worry," said Giyuu, "I will do everything in my power to avoid Tanjiro getting killed."
Suddenly, from afar, Goku heard some noises. A girl attacked Giyuu, but he quickly defended himself with his sword.
"What are you doing, Kocho?" He asked.
"Tomioka-san, are you trying to defend that boy?" Asked the girl, in a teasing tone, "he's a criminal, you know that?"
In that moment, when Goku saw the girl, a strange feeling engulfed him. His body temperature grew hotter, his cheeks blushed, and his eyes began to shine.
(What is this feeling... Do I have a fever...?) He wondered, (n-no, I think I understand...)
(I just fell in love with this girl.)
The girl had a white haori with motives that recalled a butterfly, black hair with purple shades at the end.
(She's... beautiful...) thought Goku.
"Let's bring them to the headquarters," said Giyuu. "There, his fate will be decided," said Giyuu.
"That's fine," said the girl, "we'll see what Oyakata-sama will decide."
Suddenly, she noticed Goku.
"And who might you be?" She asked.
"I'm..." began Goku, blushing, "I'm Goku Urokodaki. Ni... nice to meet you..."
"Oh, I see. I'm Shinobu Kocho, the Insect Hashira," said the girl, introducing herself.
"Are you related to Sakonji-san?" Asked Giyuu.
"N-no," said Goku, "he trained me to become a demon slayer, but we're not related. We just have the same surname."
"Kocho, I think we should bring him to the headquarters too," said Giyuu, pointing at Goku, "he fought alone against Lower Moon Five, and he's just a Mizunoe. I think he'll be useful if we take him under our wing."
"Fine by me," said Shinobu, "he's really interesting, you know?"
(She finds me interesting...?) thought Goku, blushing.
"Uh? Why are you blushing?" Asked Giyuu.
"Uh? Well, nothing..." said Goku, trying to sound casual.
"Mpfh, fine... We'll bring you to the headquarters," said Giyuu, "Sorry about that..."
Giyu hit Goku with the grip on his katana, knocking him unconscious. In that moment, Goku slowly closed his eyes and eventually passed out.
Chapter 9 - End.