Four months had already passed in Natsu's final year.
Natsu kept working hard.
His days had turned into a perfect routine. School, studying, training, friends, more studying, then sleep if his brain and body had not both melted by then. His grades were slowly improving, much to the surprise of his teachers. He even paid attention in class now. They chalked it up to a miracle and left it at that.
His training had improved too.
His morning runs were longer. He added bits of weight as he improved. Natsu allowed himself to remember what he was like before. He tried to recreate the strength he once had.
But lately, his training was stagnating. It wasn't yielding the same level of benefits. Maybe he was rushing, he knew he was. But he couldn't just keep training his physical body anymore. It was already almost perfect.
So he needed to do something more to make his quirk stronger.
Just adding more weight felt too simple. More running, more push-ups, more punches. It wasn't enough. His body was strong, but his quirk began to fall behind.
He just didn't know what he could do yet. He couldn't train it out in the open without risking causing fire hazards.
He stretched after his run. "Im sure it will just come to me." Natsu mumbled out before going to his room.
—
The answer finally came to him.
Natsu usually did not get ideas from class. He was usually just bored or trying his best to keep up. Occasionally staring out the window . But that afternoon, their teacher was talking about water pressure, and for once, Natsu found himself actually listening.
A simple drawing covered the board. A little stick figure sank deeper and deeper into the ocean while arrows pressed in from every direction.
"The deeper you go underwater, the more pressure you experience," the teacher explained. "Water pushes against the body from all sides. That is why deep-sea environments are so dangerous. Movement becomes harder, and even simple actions require more energy."
Natsu stared at the board.
Pressure from all sides and harder to breathe.
His pencil slowly stopped moving. He raised his hand.
"Yes, Todoroki" The teacher called out.
"So, technically, could someone go deep into the water to train and make themselves stronger?
"I-I suppose, theoretically, yes. Someone could do it. Quite a few quirks even allow individuals to breathe under water and take on the characteristics of sea creatures. However, even enhanced, you would only be able to go so deep under water before the pressure starts harming you. It's not something anyone can or should do."
Natsu nodded.
"Now, let's move on to currents."
The teacher kept talking, but Natsu's mind had already begun his next training method. He imagined himself as deep in the water as possible, affected by the crushing pressure of the sea. His body slowly strengthening.
Natsu's mouth slowly curled into a grin. He was getting fired up. Finally, something new.
Glowl noticed immediately. The feathers on his face puffed slightly as he leaned away from him. "Yakuto," he whispered, "Why are you smiling like that"
Natsu did not answer. But he knew why. He cursed inwardly.
Itsuki Shou glanced over, saw the look on Natsu's face, and frowned.
"No." He whispered
"I didn't say anything," Natsu whispered back.
"You didn't have to. That's the face you make when you have a crazy idea."
"It's not crazy, I promise."
"That means it definitely is."
Their teacher turned from the board. "Yakuto. Itsuki. Fuku. Is there something you three would like to share with the rest of the class?"
All three faced forward at once.
"No, sir," Shou said.
"No," Glowl added.
–
After school, the three of them stopped at a convenience store before heading home. Shou carried a bag of snacks, Glowl had a drink, and Natsu was unusually quiet as they walked. That alone was enough to make both of his friends nervous.
"Okay, fine. What is it," Glowl said.
Natsu sipped his drink. "The best training idea ever."
"Is it illegal?"
"No."
Shou narrowed his eyes. "Is it suicidal?"
Natsu paused.
"Not intentionally. It'll be fine."
Glowl groaned. "Fine. What is it?
Natsu explained his plan to his friends. "So what do you think?
Shou sighed. "Okay, that explains your question in class. That's my fault for not figuring it out.."
Glowl nodded in agreement.
"Well???"
Shou, unfortunately, made the mistake of continuing. "You know, people actually do weird underwater training stuff. I saw a video about it once. Some athletes hold their breath and train in pools to build stamina. Divers do pressure training too, but with instructors and safety gear and common sense."
Natsu turned his head slowly.
"Let me see the video."
Glowl slapped his hand over Shou's phone before he could even unlock it. "Are you sure this is smart?"
"Hey!" Natsu snapped.
"No," Glowl said. "Absolutely not. This is a crazy idea."
"Dude, you're not going to be able to stop him." Shou conceded.
Shou slowly pulled his phone back, showing Natsu the video.
"You know, you could just see this on your phone too." he mumbled.
Natsu's eyes were already bright. "So people train underwater to get stronger?"
Shou looked away. "I guess. Technically. Supposedly, the drag of the water helps train more of their muscles."
Natsu's grin widened.
Glowl covered his face. "There goes that smile."
"No, wait," Shou said quickly. "That doesn't mean you can just jump into the ocean and start doing training like this. This is in a controlled environment like a pool and maybe with a coach, I don't know."
"But think about it," Natsu said, already pacing ahead of them. "Water makes movement harder. It presses down on your body. You can't breathe. Fire gets weaker underwater, right?"
"Yeah," Shou said.
"So if I can release fire underwater, even a little, my output gets stronger."
Glowl stared at him. "I guess?."
"You're talking crazy. How would you even do that?" Shou added.
Natsu ignored them.
His mind was moving too quickly now. If water made everything harder, then that was exactly where he needed to train.
He would be able to train everything all at once.
"This is it," Natsu said.
"No, this is not it," Glowl said.
"This is how I get stronger."
"This is how you commit suicide.," Shou muttered.
Natsu pointed at them both. "Then you guys come with me."
Both of them went silent.
Glowl blinked. "Excuse me?"
"If you watch out for me it's safer right? You can stop me and check on me."
Shou opened his mouth, closed it, then groaned. "I hate that that makes sense."
"God you're stubborn." Glowl said.
Shou admitted. "If he's going to do it anyway, it's better if we're there so we can stop him if it gets too bad. We can get a rope or something and tie him to it."
Glowl stared at him like he was an idiot. 'Why are you giving him ideas?'
Natsu's eyes lit up. "A rope!"
"Well shit…"
–
The next weekend, the group found themselves in Suruga Bay, which should be sufficient for what they had planned. They met at a quiet stretch of coast early in the morning. The sun was still coming up, the wind had a slight nip, and the sea rolled in dark, lazy waves that looked far too calm for what Natsu planned to do.
However, Natsu had no fear in his eyes. He stood barefoot near the shoreline, rolling his shoulders and stretching. He had him swim shorts on.
Behind him, Shou and Glowl had come prepared. A special marina rope, some towels, a stopwatch, a first aid kit, several bottles of water, and snacks.
Glowl held up the rope. "We tie this around your waist just in case and pull you out if we have to okay?"
Natsu nodded.
"Just tug on it and we can pull you up." Shou added.
"Got it."
"If you do something stupid, we pull you up."
Natsu frowned. "Define stupid."
Glowl stared at him.
Shou pointed at the sea. "This. This entire thing that you have planned. Oh my god, I wish you just went out for villains instead."
Natsu grinned. "Oh come on, where's your sense of adventure?"
Glowl tied the rope around his waist tightly, then tugged hard to make sure the knot held. "Are you sure about this?"
Natsu looked out at the water. His expression shifted.
"School starts next year for the U.A. I have to prepare. Who knows what kind of strong people will participate." he said.
Shou and Glowl exchanged a look. The look that knew it was probably impossible to find someone stronger than their friend at 15. Who else was already fighting villains at 12 years of age.
They both sighed. Unfortunately, it was really admirable. Whenever he sets his mind to something, he gets it done.
No hesitation and no excuses. Just moving forward.
Shou sighed. "Fine. But promise this, you won't try to overdo it. Know your limits okay?.
Natsu nodded.
"Fine, I found a place near here. It's called the Osezaki cape. It's apparently an area for deep sea divers and it should work for what you're looking for. They tied the rope around his waist.
Natsu took off his shorts. Shou and Glowl both covered their eyes. Absolutely zero shame. He jumped in. He tested the waters. It was fine for the first few meters he was going down. It was still warm at 40 meters, but he felt the pressure slowly beginning to engulf him. He sunk deeper in. He could still handle far more than this
50 meters
60 meters
80 meters
100 meters
The temperature already plummeted. The cold wrapped around his legs first, then his waist, then his chest. His body immediately wanted to heat itself in response, but he forced the instinct down. Not yet. He needed to feel it first. The drag. The pressure. The way the water pushed against him from every side. It was getting harder to see. The salty water stung his eyes. It felt like traversing through cement.
The sound became a dull roar. Light scattered above him in broken silver strips. The water swallowed his body and dragged at his limbs as he kicked downward. The rope that was trailing him suddenly snapped, the sound reverberating.
Natsu forced himself deeper. It was essentially pitch black at this point
His chest tightened. His ears popped. His arms and legs felt heavy, every movement slower than it should have been.
There was a misconception regarding Natsu's underwater training. Natsu had never been trained as a diver. He did not possess years of experience equalizing pressure, nor had his body previously adapted specifically to the deep ocean. Yet he could descend to depths that should have severely injured an inexperienced human.
The reason lay within his Quirk.
Because Natsu's body had evolved specifically to consume fire and sustain combustion internally, his respiratory system had developed far beyond ordinary human limitation. His lungs, diaphragm, airways, and respiratory muscles were made to supply oxygen to a biological furnace.
However, the respiratory system did not exist in isolation. Connected to the upper respiratory tract were the Eustachian tubes. Their purpose was simple.
Equalize pressure across the eardrum.
For an ordinary human descending rapidly underwater, external pressure increases faster than the pressure inside the middle ear. The eardrum is forced inward until it ruptures.
But Natsu's Eustachian tubes had developed alongside a respiratory system accustomed to unusually powerful inhalation, exhalation, and internal pressure changes due to high heat within his body.
Natsu's body was already accustomed to pressure from within.
His internal temperature routinely exceeded normal human limits. Since his quirk awakened, whenever he stoked the furnace within, his respiratory and cardiovascular systems adapted accordingly.
However, this did not allow Natsu's internal pressure to cancel the ocean's pressure. It simply meant that pressure alone was insufficient to immediately damage him until extreme depths.
At approximately two hundred meters beneath the surface, Natsu's body was subjected to roughly twenty-one atmospheres of pressure.
200 meters.
He stopped when the pressure became impossible to ignore. His body wanted to float back up. His lungs wanted air already.
He clenched his fists and held on a bit longer.
His heartbeat thudded in his ears. He couldn't breathe. Couldn't shout. Couldn't rush forward. For once, he was stalled. He still held his breath. He didn't know how long he had been down here. The pressure was crushing him. This was a good test. He started swimming back up to what he hoped was the surface. When he felt the pressure decrease, he was elated.
–
On the shore, Shou watched the rope with tense eyes.
"How long?" Glowl asked.
"5 minutes," Shou said, checking his watch.
"That's too long."
"How long can he hold his breath?"
"A while, but this is different."
Underwater, Natsu slowly raised one hand.
A spark tried to form along his fingers.
It died instantly.
Bubbles slipped from his mouth as he frowned.
Again.
This time, he focused heat into his palm without letting it burst out wildly. Warmth gathered beneath his skin, tight and compressed. His hand glowed faintly red in the water.
Then he released it.
A small burst of heat flashed outward.
The water around his palm erupted into bubbles. His arm jerked backward from the force.
Natsu's eyes widened.
Steam.
Not fire.
The water had eaten the flame and turned it into pressure, creating an explosion. He felt disoriented. The explosion shot him down. A crazy idea came to him.
Again.
He released another burst.
Too much.
White bubbles exploded around the soles of his feet, and the sudden steam blast propelled him upward. The rope was already gone, completely destroyed from the pressure.
–
Glowl's feathers puffed. "Pull him out, this is crazy."
"Wait, was that three tugs?" Shou asked.
"I don't know, just pull. It's been too long."
They both grabbed the rope and hauled it. But they only pulled up the remains of the rope. There was no body attached to it.
"Holy Shit! Oh no, oh no, oh no!!" The duo panicked. "Was he eaten by a shark?!"
However, they were quickly relieved when they saw something emerging.
Natsu broke the surface a few seconds later, coughing and wheezing. He gasped for air as he laid down. There were some minor
"That was awesome!"
Glowl grabbed him by the shoulders. "That was not awesome. What happened to the rope?"
"It exploded."
"Oh shit, we didn't account for the pressure for the rope. That's my bad. Sorry."
"Don't worry about it. " Natsu said, wiping water from his face. He stretched a bit.
Shou stared at him. "Dude, that was insane. What was it like?"
Natsu spat water to the side and grinned.
"Exhilirating. Like a rollercoaster without a belt."
Glowl's eyes narrowed. "Definitely crazy. But did you find what you were going for?
"Yeah. It's definitely going to help with controlling my quirk and strengthening my body. It's perfect."
"Nice!"
Glowl stared at both of them. "Do not encourage him."
But Shou was already thinking. "So if you keep doing this repeatedly, you can do deeper and deeper and get way stronger right?"
"Shou."
"What? I'm saying if he does it safely."
"There is no safe version of this. Its extremely dangerous."
Natsu stood up fully, stretching his back water streaming down from his hair. Fire flickered weakly from his body, drying him.
"But I have to start slow. How long was I there for? ."
Glowl blinked. "About 5 minutes."
Natsu was stunned. "Only 5 minutes??"
Both friends stared at him.
Shou slowly pointed. "Yeah, but with how deep you were its crazy you stayed that long. You're brain must be cracked."
"It was already cracked. Probably got dropped alot as a baby." Glowl nodded.
"Shut up."
And so the training began.
The first day was rough. But he was far from done. He shot back into the water after a bit of rest.
By the end of the morning, Natsu lay flat on the sand, chest heaving, hair plastered to his face. He was breathing heavily. He felt like he did multiple workouts all at once.
Shou sat nearby with the stopwatch in hand. "Your longest hold was 6 minutes."
Natsu lifted a weak thumb.
"You almost drowned twice on that 6 minute run. "
Natsu paused.
Then slowly lowered the thumb.
Glowl threw a towel at his face. "New rule. You absolutely aren't allowed to do this alone."
Natsu pulled the towel down and grinned. "Deal."
–
By the time Natsu dragged himself home, his entire body felt like it had been wrung out.
His arms were heavy. His legs felt weak. His lungs burned in a way that was different from running, different from sparring, different from anything he had done before.
And he was grinning like an idiot.
The underwater training worked.
It really worked. So much to do.
It was perfect. But for today, he just wanted to sleep.
Natsu practically kicked the front door open.
"I FOUND IT!"
Rei jolted in the hallway, nearly dropping the laundry basket in her arms. "Yakuto!"
"Sorry!" Natsu shouted automatically, though he was already halfway through the house.
He stumbled into the living room in the same exercise clothes he had left in that morning, hair messier than usual. Shoto was sitting at the table with a notebook open in front of him, while Gray lounged on the couch with a textbook balanced lazily against one knee.
Both of them looked up.
Natsu slammed one hand on the table, eyes bright despite the exhaustion weighing down his body.
"I found my final training routine before U.A."
Shoto blinked. "Really?"
Gray slowly lowered his textbook. "Oh?"
Natsu was practically vibrating, too excited to sit still even though his legs were clearly seconds away from giving out. "I found a new training method at the beach. It's perfect. This is the one."
Shoto stared at him.
Gray stared too.
Rei, who had followed him into the room, looked between them with growing concern. "Yakuto," she said slowly, "what did you do?"
Then he smiled.
"Training."
Rei's eyes narrowed.
Natsu immediately looked away.
Shoto sighed. "That answers nothing."
"It answers enough," Gray said flatly.
Natsu ignored both of them and started pacing around the living room. His steps were uneven, but his energy was somehow still overflowing. "I'm telling you, this is it. If I keep doing this until the exam, I'll be way stronger. Then I'll kick everyone's ass at U.A."
Shoto's expression shifted from concern to thoughtfulness. "You're sure?"
"Yeah." Natsu's grin sharpened. "My whole body feels like it got beat up."
Gray sat up fully. "Interesting."
Rei looked like she wanted to ask several more questions, then seemed to decide she probably did not want the answers. She hugged the laundry basket tighter against her chest. "Please do not do anything dangerous okay?"
Natsu gave her a thumbs up. "I won't."
No one in the room believed him.
Still, there was something different about him. He was exhausted, almost swaying on his feet, but his eyes were bright and focused. He had found something that pushed him in a way his normal training had not, and Gray could see it.
Natsu looked way more excited than usual. He must have really found a great training method if it got him like this.
Gray leaned back into the couch and began thinking.
Natsu squinted at him. "You're thinking."
"I do that. You should try it sometime."
Gray looked away, but he had an idea.
Natsu was reckless.. But there was this new side to him now that was way more focused. Natsu had been grinding every single day. Studying. Training.
And now he had found even more extreme to work on.
Gray had been training too. His progress was going as he expected. His constructs were far more precise. His output had increased exponentially, but he felt like he was reaching a bottleneck. He felt stuck.
His fingers twitched slightly against his knee as he remembered the thin thread of ice he had made by accident when he pushed himself. He tried to recreate it but it wasn't shaping to be how he wanted it.
Maybe the city was the problem. He recalled his training once again with his master. His master Ur had made sure he focused on fundamentals and that in order to control ice perfectly, you had to become one with the environment.
Maybe it applied here as well? Maybe he needed to go somewhere cold?
Somewhere the cold was everywhere.
Natsu finally gave up on standing and flopped onto the floor with a heavy groan, arms spread out.
"I'm doing it again next weekend."
"It's not too dangerous is it? You should be careful. If this goes wrong, you might not be able to apply.
"I'll make sure I am safe. It's not a big deal."
Gray stood suddenly.
Natsu lifted his head again. "Where are you going?"
"To check something."
"What thing?"
"School thing."
Gray ignored him and walked down the hall.
When he reached his room, he closed the door behind him and opened his computer. The program page was still there, waiting from the last time he had looked at it. It was something he casually found in the hallway on a board. He grabbed it without thinking too much. It seemed very interesting.
His private school had far more resources than public schools. It provided great opportunities for people who wanted to be heroes in the future. Some of them could help you get a nice recommendation into a hero school. It was optional, but some of the students did it to gain experience. Shoto was already going to Endeavor's office from time to time. However, most of the time it was just helping heroes with paperwork since they were strictly prohibited from doing any sort of hero work.
He had no interest in wasting time making copies or sorting forms. But one listing had caught his attention a few days earlier, and now he found himself reading it more carefully.
It was a support assignment connected to a pro hero's agency and an environmental research team stationed in Antarctica. It was not a real hero internship. Students would help with administrative work, supply logs, communication records, and research documentation. It was extremely boring.
On paper, anyway.
Gray stared at the location again.
Antarctica. It was the perfect location for the kind of training he had in mind.
He leaned back in his chair, eyes narrowing.
Natsu had his final training session planned.
Maybe Gray had just found his.
A recommendation was required, but that would not be a problem. His grades were high. His teachers liked him. He had stayed out of trouble, at least officially, and his record was clean enough that no one would question the application.
Gray clicked the page open.
One month.
He would go there, finish the assignment, and use every free second he had to train.
And when he came back, Natsu would not be the only one with a new trick.