Male OC X Kimetsu No Yaiba / Demon Slayer

Sagiri Mountain

No one's POV

Sabito, Makomo, and Giyu finished their training for that day and are enjoying their lunch break at Sakonji Urokodaki's small house at the base of Sagiri Mountain.

"Sabito-Kun, you're eating too fast. You might choke." Makomo warns Sabito about the consequence of his bad habit.

"MPPHH! But Urokodaki-san ...*Chomp! Chomp!*... tells us he wants us to...*Gulp!* follow him! We must hurry up!"

"Sabito-kun, Makomo-chan is right."

"Eeeeh?!! Giyu-Kun! How could you took her side!"

"It's for your own sake, Sabito-Kun." Giyu sips his green tea.

Sabito's mood turns gloomy.

...

*Birds chirping*

*Sound of their footsteps*

"Urokodaki-san, this route is new to us. Where are we going?" Giyu asks.

"Your final task. You have to finish it or I won't let you participate in the next Final Selection."

None of them said a word. Each of them keep wondering what the test would be. As they keep walking, they hear a voice.

" Dear spirits of Urokodaki's fallen students, you all may now rest in peace because I, Yoru Rengoku, had slain the morphed hand demon who was responsible for your deaths. Your regrets and worries shall disappear for there's nothing to worry about anymore. If you still worry about Urokodaki's current student, I shall tell you that I already had a plan. Rest well in heaven."

They search for the owner of the voice and found a boy around their age that has golden hair with red tips, wearing dark flame-like haori and an unusual mask. He's sitting on the ground while praying. What makes their blood run cold is they could see some spirits of Urokodaki's previous students, smiling and thanking him before they disappear into the mist. The boy waves his hand and just stands there.

"You're here." Yoru's response makes them flinch. "I've been waiting for your arrival, Giyuu, Sabito, and Makomo." Hearing their name from an unknown person, they draw out their sword.

"Who are you?!! How do you know us?!!"

"Wow. You're dumber than I thought. I thought that I already said my name out loud and yet you still ask me. Pathetic."

An irk mark appears on his head. "WHAT DID YOU JUST CALL ME YOU BASTARD?!!"

Yoru just sighed, this angers Sabito even more. Before Sabito could attack Yoru, Urokodaki grabs his yukata from behind. "That's enough, Sabito. And you, you must be Shinjuro Rengoku's child. I heard that you passed the Final Selection, which surprised me. You just turned ten." The news of me passing the Final Selection surprises the trio. Plus, I'm younger than them. "...But, what are you doing here? Aren't you supposed to return home?"

"I already sent my Kasugai crow to inform my father. I'll return right after I had a few words with you."

"...Go on." Urokodaki agrees to listen.

"The demon that you caught in the previous era kept a grudge on you and swore to himself to kill your students. He became a morphed demon. The reason your students died is that they failed to kill him. His neck is a whole lot harder than your pathetic 'final task' boulder. I advise you to use a larger boulder. Choose the one that you think they might not able to slice. And that's all from me. I'm leaving." 

Yoru turns around but Makomo stops him by standing in front of him. "Hold on! How do you know our names?!! And how do you know their deaths?!!"

Yoru's POV

Sigh... this girl is such a pain. I want to go home already. Kyojuro and Obanai have been waiting for my return. I miss them already.

"My father, Shinjuro Rengoku, is the Flame Pillar. Your names are no secret to the Demon Slayer Corps. Since I passed the Final Selection, I'm now their official member. Second, that sack of garbage boasts how many Urokodaki's students he had eaten. He tells me their final moments of failure and such to lower my fighting spirit. But I managed to kill him. I come here to tell the spirits about my victory so that they can finally rest in peace. Now, excuse me, I'm going home."

"Wait, Rengoku. There's one more question I want to ask. The Final Selection just end yesterday morning. HOW did you get here so fast?"

Crap! Urokodaki's question endangers my secret! Think, Yoru! "I... use a shortcut." Damn! Is that the best excuse I could think of?!!

"Huh? A shortcut?"

"...Yes. I use the forest route instead of the normal road. I... can jump pretty high."

"Hmm... really? Would you be kind enough to show us?"

Crap. Oh well, showing a little bit won't hurt. "Okay..." I shunshin to a tree and jump from one to another tree around them. For the final performance, I jump really high in the air and do some air flips and skydiving. I grab the tree branch with my hands and swing myself towards my original spot. I unsheath my sword in the air and land gracefully. I twist my body and point my sword near Makomo's neck. Sabito and Giyuu were alarmed by my action. Makomo was too stunned to say anything. They both start to attack me using Breath Styles. Before they could finish, I shunshin behind their back and use the handle of my sword to knock out both of them. 

Heh! Take that, Giyu. This is payback for what you did to Tanjiro in episode 1!

Sorry for getting you in this mess, Sabito, Makomo. But, if you two can't kill that morphed demon, then how on earth can you two kill the Twelve Demon Moons? You must realize that you're all still weak to face any of them. "Next time we meet, I expect you all to be stronger than today. We might face the Twelve Demon Moons in the future. I don't want my future comrades to become their midnight snack. Understood?"

Makomo just nods. Her eyes are still wide open. Sakonji Urokodaki wants to say something but I cut it.

"Before you ask anything more, I'll tell you that I did extra training besides my father's training. That's all. May I go home now, Urokodaki-san?"

"Yes, you may, Rengoku. Thank you. Now, the spirits of my previous students finally could rest in peace. I'm sure that you'll become a Pillar in a short amount of time."

"Yeah. That's my current goal. I'm gonna create history by becoming the youngest Pillar. Farewell, Urokodaki-san. Train them to death."

No one's POV

Urokodaki sweatdrops at Yoru's last word. Yoru then shunshin and jumps from tree to tree before finally disappear from his sight. He then turns his head towards his students. Looks like they need more training. Urokodaki didn't want any of his students to die in vain anymore. 

"I've decided... I'm going to train you all more seriously."