Chapter 8: Vows and Udon
A few days later.
The night was deep, and the campfire beneath the cliffside crackled rhythmically.
The two had just finished a battle. Splattered with demon blood, they were taking advantage of a rare quiet moment to rest and maintain their Nichirin Swords.
After nearly ten demon ambushes, Natsuya's Breathing Style was finally approaching the threshold of Level 3. Since he had a surplus of Achievement Points, he decided it was time to pull the trigger and upgrade his Wind Breathing.
A 30% conversion loss? Whatever. I need the stats now.
Ignoring the spacey girl roasting a fish across from him, Natsuya summoned his System Interface.
Alright, System. Time to show you the fruits of my labor.
[Allocate Points!]
A single Achievement Point—the condensed essence of Natsuya's hard work—was dumped into the Wind Breathing panel. It transformed into an invisible heat, pushing his experience bar upward at a breakneck speed.
In an instant, all his effort coalesced into tangible growth.
[Wind Breathing LV.2 → LV.3]
[Adept→Proficient]
[Proficiency: 13/2000 (+325)]
[Power Level: 37 → 54]
Body: 17→ 26
Tech: 9 → 15
Mind: 11→ 13
[Your mastery of Sword Forms has increased!]
[Active Skill Unlocked: Total Concentration Breathing]
[Total Concentration Breathing: By forcefully drawing massive amounts of oxygen into the lungs, the user drastically enhances their heart and lung function. This hyper-oxygenates the blood in a short burst, granting physical abilities that far surpass human limits.]
Oh?!
The Level 3 milestone came with a bonus derivative ability. He looked at the skill description and immediately understood.
It's basically 'Gear Second' from One Piece!
He got the concept immediately. At the same time, he began to calculate the progression curve for future levels.
500 XP for Level 1, 1000 for Level 2, 2000 for Level 3...
If the pattern held, the next levels would be 4000, 8000, 16,000... reaching Level 10 would require a total of roughly 500,000 experience points.
After doing some quick mental math and scratching a few figures into the dirt with a stick, he reached a conclusion.
To get from Level 1 to Level 10 would require approximately 1,600 Achievement Points based on his current Wind Breathing conversion rate.
Hmm...
And that was just for one Breathing Style. If he tried to master multiple styles through daily training alone, he'd probably be 80 years old before he maxed them out.
As expected, the end of all 'effort' is just a prompt to 'top up' your account.
He weighed the efficiency: Level 10 cost 1,600 points, Level 9 cost 800, and Level 8 was only 400.
Who knows if this game even has 400 different Life Skills I can grind?
This confirmed his theory: finding a Breathing Style with higher compatibility was the only viable "Meta" strategy. In the late game, every 10% increase in compatibility would save him dozens of Achievement Points.
Ideally, he should dip into other Breathing Styles too. Dumping a few points into a secondary style would provide a small "stat dump" for his base attributes. Even a "frog's leg" is still meat, after all.
As for the newly unlocked active skill... Based on his years of gaming, he was certain that further upgrades would unlock even more powerful versions of Total Concentration. He was genuinely curious to see how far this "physics-defying" system could go.
While Natsuya was lost in thought, Seiko silently handed him a roasted fish.
"Kokonoe-kun? I don't know what you're thinking about, but... in that last second, you felt different. Like... much stronger?"
After a few days of life-and-death struggle, Seiko's mindset had stabilized, but she still retained that somewhat timid, "spacey" vibe.
"Is it because these past few battles helped you refine your Breathing and sword techniques?"
Natsuya didn't deny it. "Yeah. The combat and training over the last few days allowed me to 'level up'... I mean, I've had a breakthrough."
This NPC's intuition is pretty sharp. Does the stat jump trigger hidden dialogue?
"Hey, Kokonoe-kun?"
"Why did you join the Demon Slayer Corps?"
The girl rested her chin on her hands, tilting her head as she looked at him. The gentle orange glow of the fire painted a soft flush onto her youthful face.
"Me?"
"Mostly to kill every demon I see. Or maybe just to find the strongest one and put him in the dirt."
He wasn't sure what the end-game main quest would look like, but action game plots usually weren't that deep. Natsuya took a bite of the fish.
It wasn't good. It was over-charred, unseasoned, and hadn't been marinated. He should have done it himself to grind his [Cooking] proficiency.
"To kill... all the demons?" Shock flickered in Seiko's eyes. She lowered her head, her voice tinged with a complex emotion. "That's amazing... A genius swordsman like you might actually be able to do it."
"What about you?" Natsuya asked, watching his Hunger Bar refill. "Why are you here? You looked like a mess when we first met. Didn't you prepare yourself?"
The girl's expression dimmed.
"How can anyone ever be 'fully' prepared for this?"
"It's just... even if I'm not ready, I have to do something."
"My family... my little sister... they were all killed by a demon."
"I want revenge."
Hearing the word "sister," Natsuya went silent for a moment. He remembered his own character background—it was basically a carbon copy of hers.
The "Vengeance for the Slaughtered Family" archetype.
But he quickly realized that this was probably the most common story in the Demon Slayer Corps. Survivors of demon attacks, betting their lives on training, charging at monsters with nothing but a human body.
It was a cliché, but it was a classic for a reason.
Natsuya's gaze softened. For once, he didn't skip the dialogue.
"Hey, Seiko... you'll get it done."
"The revenge. Killing those monsters."
"Even if you don't make it, it's fine. Because there will be wave after wave of Slayers coming after you, pushing toward that same goal."
"And even if they all fail..."
Natsuya flashed a smile—a smile full of the absolute confidence only a player has when they know they're going to win.
"I'll finish it."
"Huh?"
Seiko looked up in surprise, unable to believe this normally distracted boy could say something so profound. A surge of emotion hit her, and her eyes grew warm.
"Th-thank you for the encouragement, Nat... Natsuya-kun."
Natsuya laughed. "Until then, you better train like your life depends on it. It's always better to settle your own grudges personally."
"Using a human body to challenge the demons... that's the will of humanity. It's the anthem of courage."
The girl nodded solemnly. "I will do it."
"I'll be watching, then," he replied cheerfully.
Seiko finally let out a small smile. The haze of doubt and hesitation that had been following her finally began to dissipate. Natsuya-kun really is a special person.
The campfire burned quietly, lighting up their young faces. She idly poked at the embers with a stick, watching the sparks dance upward into the night sky.
"After we pass the selection," she said softly, "I want to go eat a hot bowl of Udon."
"A big bowl, with two soft-boiled eggs."
"Want to come with?"
Natsuya thought about the taste of Udon and immediately shook his head.
"No way. We're eating BBQ."
If possible, he wanted to find a place to learn more advanced culinary techniques. He'd already noticed that the tastier his meals were, the faster his [Cooking] proficiency increased.
Seiko wasn't disappointed by his rejection. She covered her mouth and giggled.
"Fine. We'll eat BBQ first."
"Only if you're paying."
"It's a deal."
Just as the warmth of the fire began to ward off the chill of the night, a piercing demon howl echoed from the distance, followed by the shouts of Slayers in combat.
The two immediately stopped talking.
They gripped their swords, their eyes turning sharp and focused. Seiko patted the dust off her skirt and stood up. "Looks like break time is over."
Natsuya stood up as well, rolling his shoulders and neck.
"Let's go. Back to the grind."
Seiko didn't understand the last word, but she got the gist. She nodded and followed him into the shadows.
"Don't forget our promise!"
Natsuya called back, "If I forget, I'll buy you the Udon!"
Seiko laughed, "And the two eggs!"