Goku had just defeated Mukago, Lower Moon Four, thanks to his Sun Breathing, which nobody saw, fortunately. Due to his efforts and struggles, the boy fainted after the battle.
The day after, in the morning, Goku woke up.
"Ugh... What happened...?" He muttered, while staring at the ceiling. Suddenly, from the door, Hiroshi appeared inside the room.
"You fought a Lower Moon and won, Goku," he said.
"H-Hiroshi-san!" Exclaimed Goku, "Did you bring me here?"
"I did," said Hiroshi, "this is my room, don't you remember?"
"Of course I remember..." muttered Goku. Suddenly, he heard a noise; It was Rin, once again.
"Caw! Caw! Breaking news, Goku! You've just been promoted to Mizunoe! Caw!" She said.
"Mizunoe? What does it mean?" Asked Goku.
"It means you've been promoted," explained Hiroshi, "in the Demon Slayer Corps, there are ten ranks. You were a Mizunoto, the lowest rank. But now, you've been promoted to Mizunoe, the rank above the Mizunoto."
"Oh, I understand..." muttered Goku.
"That's not all!" Exclaimed Rin, suddenly, "reach Mount Natagumo for your first mission as a Mizunoe! Hurry up! Caw!"
Goku scratched his head, clearly annoyed.
"Another mission... In less than twenty-four hours, I've killed two demons, and I'm gonna kill the third, after this mission..." he said.
"Let's look at the positive side: You're a Mizunoe now, Goku!" Exclaimed Hiroshi.
"Yeah, you're right, Hiroshi-san..." muttered Goku, getting up and opening the window, "fine, I'm gonna reach Mount Natagumo or whatever it's called... Let's just hope not to die in the process though... See you soon, Hiroshi-san."
Goku threw himself from the window, getting outside the house.
"Hey, Rin! Where's Mount Natagumo?" He asked.
"Northwest! Caw! Northwest!" Croaked Rin.
"I see... Mount Natagumo, here I come..." said Goku. sheathing his sword in its custody and started run towards northwest to reach Mount Natagumo.
Hours later, when the sun went down and the moon began to show, Goku arrived at the foot of the mountain.
"So this is Mount Natagumo... I can't believe it took all the day to come here..." he whispered under his breath. Then, Goku made his first step on the mount. The silence was absolute, the only sound the rustling of leaves.
(Is there really a demon? Or was it killed before my arrival?) wondered Goku. Then, suddenly, he got cornered by other slayers.
"What the hell... Are they attacking me?" He wondered.
One of the slayers jumped on him, whirling his katana towards him, but Goku managed to dodge. Here, Goku noticed something: The slayers were commanded by webs. So... was there some kind of spider demon here?
(Someone's manipulating them...) he thought, "Flame Breathing: First Form -- Unknowing Fire!"
Goku launched himself forward, escaping from the circle.
(If I manage to find and kill the demon who's manipulating them,) thought Goku, (I'll free them all.)
Suddenly, while running, Goku bumped into a slayer.
"Ops, I'm really sorry..." said the slayer.
"No problem. Are you... possessed?" Asked Goku.
"No, I'm not, for now," said the slayer, "are you a Mizunoto?"
"Nope. I'm a Mizunoe, the rank above," replied Goku.
"Really? Finally... they sent someone who's not a Mizunoto..." said the slayer, in disbelief, "Please, kill the demon on this mountain..."
"I will," said Goku, "just stop kneeling."
The slayer got up and nodded. Then, Goku left, continuing to search for the demon.
(If this demon can manipulate my comrades' will with his webs... Then I suppose it won't be easy... What if it's another Lower Moon...?) wondered Goku.
Elsewhere, on the mount, a little slayer was fighting against a demon. Crimson hair, hanafuda earrings and a green and black haori. It's a boy Goku already met during his journey: Kamado Tanjiro.
Tanjiro had cuts on his face, and blood splintering all over his body. Behind him, there was a girl with a bamboo in her mouth. Suddenly, the demon Tanjiro was facing approached.
His entire body -- hair, face and skin -- was white, with the only exception being his eyes, which were red. On the left eye, the demon had the kanji of 'Lower Five,' symbolizing that he's indeed a Lower Moon. His name was Rui
"C'mon, slayer, give me your sister... I promise I won't hurt her... at first," said the demon.
"Like hell I will! I'm not giving Nezuko to you!" Yelled Tanjiro, holding his broken katana with both hands.
"Well, I guess I have no choice but to kill you, then..." said Rui.
"Not if I manage to cut off your head first!" Said Tanjiro.
"Are you seriously thinking... that you can beat ME?" Yelled the demon, swinging his hand. In a blink of an eye, Tanjiro saw Nezuko tied up in the air by thousands of webs.
"Quiet down. This won't be enough to kill her. At least, I think so..." said Rui.
"Let her go, you monster!" Yelled Tanjiro, throwing at Rui, "Water Breathing: Tenth Form -- Constant Flux!"
"It's futile..." said Rui, calmly, as his webs reached Tanjiro. But the boy cut them off with his Water Breathing.
"Do you really think these webs are at their maximum level...?"Asked the demon, filling the webs in his fingers with blood.
"Blood Demon Art: Cutting Thread Cage."
In a fraction of second, thousands of red webs circled Tanjiro, making him unable to escape from every distance.
(N-no... This is the end... I'm going to die...) thought Tanjiro, closing his eyes and preparing to take the hit.
But suddenly, just like as if the fate listened to Tanjiro, the miracle arrived.
Goku arrived just in time to see the situation, and without hesitating, he jumped in the air and exclaimed, "Flame Breathing: Third Form -- Blazing Universe!"
SLASH!
All the webs got cut clean off. Tanjiro was confused.
(Who... Who did that...?) he asked to himself. Then, he turned his head, and saw a guy with a light blue haori with orange flames at the edge, mid-length hair and a yellow and black katana. In that moment, Tanjiro recognized him.
"You're... You're the one from the drum's mansion!" said Tanjiro.
"Yes," answered Goku. "You're Tanjiro, right?"
"Yes, I am..." replied Tanjiro, "what was your name?"
"Goku Urokodaki," said Goku. Then, the boy looked up to see Nezuko in the air, tied up by webs.
"Do you... know that girl?" He asked.
"Yes... She's my little sister..." answered Tanjiro.
"Oh, I see," said Goku, "I apologize in advance if I absentmindedly hit her."
"First Form -- Unknowing Fire!" He exclaimed, and in a blink of an eye, the webs severed, and Nezuko was freed. The girl fell from the sky, but Tanjiro managed to reach for her and avoiding the impact with the ground.
"Tanjiro, I'll handle it from now on. You think about hiding your sister from this guy..." said Goku.
"Are you sure about that? He's Lower Moon Five..." said Tanjiro.
"I fought Lower Moon Four and won yesterday," said Goku, "so if he's weaker than Lower Moon Four, I can actually win..."
Meanwhile, Rui was listening.
(He... fought Mukago? And defeated her? Who's this guy?) he wondered, (Could it be that... he's a Hashira?)
Suddenly, Nezuko walked towards Goku and looked at him.
"Mh..." she said.
"Uhm... Why is she staring at me like that?" Asked Goku.
"She does this often with the new faces..." answered Tanjiro. Then, without warning, Nezuko jumped and hugged Goku.
"Uhm... Thanks, I guess..." said Goku, quite embarassed.
"I think it's a way to say thank you for having freed her," supposed Tanjiro.
"Oh, uhm.. Yes, no problem, Nezuko-chan..." said Goku, breaking the hug.
"Now go. Do as I said," he said, watching Tanjiro from the back of this shoulder, "once I've finished with this one, we're gonna go help the other two guys who were with you. This time, I'll join you, just like I promised..."
"U-Understood! Let's go, Nezuko!" Said Tanjiro, hiding alongside Nezuko.
"So, what's your name, demon?" Asked Goku.
"My name is Rui," replied Rui, "I'm Lower Moon Five. And you are?"
"I'm Goku Urokodaki, age nineteen, I'm a Mizunoe and I use Flame Breathing!" Axclaimed Goku, pointing himself.
From behind a tree, Tanjiro was holding Nezuko, protecting her, and listening to Goku at the same time.
(He's a Mizunoe?) He repeated, (he's higher than me, in rankings... Maybe he can really win...)
Chapter 8 - End.