Unnamed island...
"What did you say?!" Garp grabbed Ace and roared.
"I said, I don't want to be a Marine, I want to be a pirate!" Ace repeated, picking his ears, ignoring Garp's fury.
"What nonsense are you talking about, you little bastard!" Garp gritted his teeth, glaring at Ace.
"I'm not talking nonsense. I just want to become a pirate," Ace continued provocatively.
"Very good! I will correct your bad habits now! I will never let you become a pirate!" Garp clenched his fists and roared.
Ace's eyes narrowed as he saw Garp clenching his fists. He had deliberately provoked Garp to engage in direct combat training, aiming to reach his physical limit and activate the combat turtle breath method to strengthen himself quickly. Training alone was no longer enough to push his body to its limits, but a fight with Garp would certainly do the trick.
"Get ready, Ace!" Garp shouted, throwing a punch.
"Whoosh!" Ace's body turned into flames, quickly moving away.
"Has he already mastered this level of elementalization?" Garp narrowed his eyes at the retreating flames. Most people needed time to adapt to a Devil Fruit's power, but Ace seemed to use the Mera-Mera Fruit effortlessly, just moments after eating it.
"It seems I need to be more serious. Ace, don't think that eating the Logia Devil Fruit will protect you from all attacks. Taste the iron fist of my love!" A black aura surged onto Garp's fist, enveloping it in Armament Haki.
"Whoosh! Whoosh!" With a harsh tread, Garp's body turned into an afterimage, appearing above Ace in an instant using Marine Six Styles, Shave.
"So fast!" Ace marveled, looking up at Garp. He quickly concentrated the power of the Mera-Mera Fruit into his right fist, turning it into flames. He punched hard.
"Fire Fist!" Ace's blazing right fist roared towards Garp like a fire dragon, the heat causing the air around it to ripple.
Garp's eyes flashed with surprise at the sudden flames. "Is it so powerful just after eating the Mera-Mera Fruit? Sure enough, Ace must become an excellent Marine!" Garp calmly brought down his jet-black fist, ordinary compared to Ace's fiery punch, but...
"Bang! Bang! Bang!"
"Hiss! Stinky old man! You hit so hard!" Ace's loud curses echoed across the island.
...
Ace lay on the ground, panting heavily, feeling like every cell in his body was drained. Beside the fire, Garp was processing the fish and Sea King caught by Ace.
"Hahaha, Ace, your ability is great for barbecues! Hahaha," Garp laughed, looking at the exhausted Ace.
"Stinky old man, don't be proud. Sooner or later, I will beat you," Ace muttered, every muscle in his body aching. Getting hit by Haki really hurt.
Ace wasn't surprised at being completely defeated by Garp. After all, he was facing one of the strongest fighters in the world. But Ace had achieved his goal. He felt on the verge of activating the combat turtle breath method and sensed that this time's harvest would be greater than any before.
"Oh? I'm looking forward to that day, hahaha," Garp laughed.
"Well, it's almost done. I..." Before Garp could finish, Ace, who had been paralyzed on the ground, suddenly leaped to the side of the roasted Sea King, stuffing his mouth with food. The Sea King, hundreds of meters long, disappeared at a speed visible to the naked eye under Garp's stunned gaze.
"Hey! Brat! Leave some for me!" Garp shouted.
At night, on the unknown island...
Beside the campfire, Ace was sound asleep, having used the Combat Turtle Breathing Technique. His body expanded like a huge balloon, and next to him lay the skeletonized remains of the Sea King he had consumed. Garp watched silently as Ace's body rapidly shrank with each breath. In no time, Ace returned to his normal state, but it was evident he had grown taller and more muscular.
"Were they all absorbed in an instant?" Garp muttered, retracting his Observation Haki. Ace's terrifying physical talent was unmatched, even by the likes of Kuzan and others. With the Mera-Mera Fruit and Conqueror's Haki, Ace's future was unimaginable. Garp grinned, thinking about the more powerful iron fist of love he would use to ensure Ace understood there was no future in piracy.
...
The next day, as soon as Ace opened his eyes, he felt a change in his body. He clenched his fist, feeling a surge in power.
"Your understanding is heaven-defying! You can perfectly sense the changes in body strength, and your physical fitness has been enhanced by 30%!" a voice in his mind announced.
Ace smiled with satisfaction. "Sure enough, actual combat is the fastest way to increase strength."
"Hey! Ace, are you awake? Ready for a new round of teaching from me, grandpa?" Garp called out, clenching his fists and laughing.
"Stinky old man, don't be so proud!" Ace shouted, rushing forward with his fist turning into flames.
"Hahaha!" Garp wrapped his fist in Armament Haki and faced Ace head-on.
...
Just like the day before, Ace collapsed on the ground, breathing heavily. Garp noticed the significant improvement in Ace's strength, speed, and the power of the Mera-Mera Fruit.
"In just one night, his strength increased by 30 to 40%," Garp thought. This incredible growth rate strengthened his resolve to train Ace into a great marine. He saw the potential for Ace to surpass even his father, the Pirate King Gol D. Roger.
"How about it, Ace? Have you given up on becoming a pirate?" Garp asked, rolling up his sleeves and laughing.
"By the way, Ace, does it hurt when this power hits you? This is called Armament Haki. With this power, you can hit Logia's Users . If you become a Marine, grandpa will teach you this power."
Ace, lying on the ground, showed great disdain. "Who cares about this mediocre power? The Marine's powers are not flashy at all and can't compare to my Mera-Mera Fruit. I don't even want you to teach me anything."
Although Ace was thrilled, he pretended to be disgusted. Armament Haki was strong, but Ace was more interested in flashy moves.
"Mediocre?" Garp's mouth twitched. Known throughout the sea for his iron fists, Garp couldn't believe Ace considered them ordinary.
Suddenly, Garp thought of something. Ace, being only seven, was naturally drawn to flashy moves. If Garp could show him the most powerful and gorgeous power in the world, he might steer Ace away from piracy.
"Oh? Marines doesn't have any fancy moves? Ace, let me show you the most powerful and gorgeous power in this world." Garp's eyes flashed a thick purple-black color. He then focused intently, and in the next moment, purple-black lightning illuminated the sky.