Male OC X Kimetsu No Yaiba / Demon Slayer

Breath of Flame

Ruka finally gave birth to a baby boy. Father wraps the newborn baby with a white cloth and shows the little cutie to us.  He also inherits his father's hairstyle and other facial appearance. Being an excited fan I am, I incidentally muttered "Senjuro Rengoku" out loud. Realizing my error, I cupped my mouth with both of my palms. Ruka and Shinjuro seem surprised at my response. My action also attracts Kyojuro's and Obanai's attention who is sitting by my side.

"You want to name your new brother, Yoru?" Shinjuro questions me.

"Ahh... I... yes..." I lower my head because I'm embarrassed.

"Fufufu~ That's not a bad name. From now on, his name will be Senjuro Rengoku!" Ruka holds Senjuro dearly.

Sigh... now I'm the one who gave my little brother his name. So much for laying low. Forgive me, Lord Lucky.

"Oniichan! Not Fair!" Kyojuro pouts.

"Shh... You might scare him otouto."

"Oniichan! If you call me 'otouto', then, what will you call him?"

I raise my head and staring the ceiling. What will I call Senjuro? Hmm... I've decided. "I'll call him Senjuro-Kun... because I named him."

Everyone else sweatdrop. 

"Hey, Obanai-Kun? Do you mind that we address you like that even though you're a year older than us?" I ask politely.

"I don't mind, Yoru-Kun. Besides, you two are taller. It's normal for someone mistaking my age."

...(awkward silence)...

Oh, that's why. Alright! Let's get back on the topic. With the cheat trick Lord Lucky taught me, I'm going to excel in the Breath of Flame training! Sorry again Lord Lucky, but I'm going to become the youngest pillar in history!

Meanwhile in another world...

Lord Lucky just finished conquering another dungeon and received the title 'Demon Lord'. "WHAT?!! I DON'T WANT THAT DAMN TITLE!!! I'M NOT EVEN A DEMON!!!"

*System: You are one now, considering your crazy high status.*

"GAAH! I NEVER WANTED TO BE IMMORTAL! I JUST WANT TO BREAK THIS DAMN CURSE! WHY IS THAT SO HARD TO ACHIEVE?!!"

*System: You are now qualified to attend the annual Demon Lords meeting at The Castle of...*

"I DON'T GIVE A DAMN! I'M NOT GOING!!!"

...

(Training Ground)

This is it! This is the moment I've been waiting for!

"Boys! You're going to learn the Breath of Flame from me!" Shinjuro is smirking at us.

"Shinjuro-san, what if I can't use the breath?" Obanai asks him.

"Then, you need to use another breath or create your own! Now, watch my movements very closely. I'm going to demonstrate the first form!" Shinjuro takes his stance, "Breath of Flame, First Style: Unknowing Fire." Shinjuro charges towards a training dummy at high speed and decapitates in one or multiple slashes.

"WOAH! SO COOL! Right? Oniichan? Obanai-Kun?"

"Indeed... Shinjuro-san is amazing."

While they busy admiring Shinjuro, I also take my stance. Without any warning, I performed my attack. "Breath of Flame, First Style: Unknowing Fire." I use Madara's fire breath Jutsu and apply it to my sword-wielding technique. The fire is slightly larger than Shinjuro's fire. I managed to decapitate the training dummy with one slash. All attention now is directed towards me. Shinjuro smirks while Kyojuro's mouth widens and Obanai's eyes largen. "What's next?"

"Heh. You really are a prodigy Yoru! I bet you will be the youngest pillar in history!"

Well... that's my current goal.

"Get ready Yoru! Next moves won't be easy!"

"Bring it on."

Kyojuro and Obanai just watch Yoru from afar. "No way... oniichan is ahead of us!"

"We must train harder in order to catch up with him. Let's work together, Kyojuro-Kun."

...

I nailed it! I've mastered... I mean cheated.... the Breath of Flame! 

"Yoru, now for the final test, you must slice this boulder! Then, I'll let you participate in the final..."

Shinjiro's speech being disturbed by Yoru who already sliced the boulder. His mouth agape.

"Do you have a larger one?"

"Ah... y... yes! That one!" Shinjuro points to a larger rock nearby a waterfall. "If you managed to slice that..."

Again, Yoru managed to slice the rock in a perfect half. Shinjuro is slightly horrified of his son's crazy strength. He thought that Yoru's training might be too harsh but in reality, Yoru is training secretly in his dream with his mentor, Lord Lucky.

"How..."

"Ah! I did some extra training. Nothing more." Yoru tells half-truths just like what his mentor told him to. "Father, what should I participate?"

"Ah... the... final selection! You must pass it in order to become an official demon slayer. Yoru, you must come back alive!" His stare intensifies. He really does worry about me. I'm only ten and I'm going to the final selection. Senjuro was just born yesterday and he might not see me in the future if I died. Keyword. IF.

"I promise I will come back alive and well, father."

Shinjuro eyes are glistening with tears. He hugs me tightly. VERY TIGHTLY. It's a fortune that my bones didn't break.

Kyojuro and Obanai also come. They are confused why Shinjuro is upset. When Shinjuro told them I'm going to the final selection, they start crying and also hugs me with their bone-crushing hug... Nah, I'm just exaggerating. My bones didn't break.

We go home to tell Ruka about this. She really didn't expect me to participate in the final selection this early. She seems hesitant but after Shinjuro tells her about my accomplishments during my training, she finally agrees.

Shinjuro gives me my haori! It looks so awesome! It has a black-blue gradient pattern and purple flame-like ridges at the end. My sword, or what they call Katana is slightly different than Kyojuro's Katana in the original anime.

Kyojuro still has teary eyes. "*Snif!* Oniichan! You did promise not to leave me, remember? *Hic!*"

I ruffle his hair. Oh, how I'm going to miss him very much. "Otouto, if I stay, more lives will be in danger. I can't let that happen."

His eyes become tearier. Obanai looks away so that I won't see his crying face. Sigh... departing is sure heartbreaking. I grab them into a group hug. "Even if we're different, I would never forget any of you, because you're all precious to me. So, please wait for my return. Promise?"

They return my hug much tighter than before. I have to admit, this hug is too much to handle!

"Enough, you two. Yoru has to go now."

With a heavy heart, they finally let me go. I walk towards the front yard and wave my hands up in the air. Kyojuro and Obanai also did the same. I use gestures now to show how I feel because my unhelpful poker face won't team up with my feelings. With a satisfied heart, I turn around and head to my destination. Fujikasane Mountain!