The next day Garp kept his promise and showed them all the cool marine skills he knew first thing in the morning. Which turned out to be quite a few, the flying skill he called geppo but didn't explain how it worked at all. He just gave the boys a close up demonstration before he moved on to the next skill.
Tekkai was the next one Garp showed the boys, it was a little harder to demonstrate the skill to them. But after letting the boys punch him a few times with it off and then being punched while he used it worked as a good example. Garp also used it to break a large rock into pieces. As far as the boys could tell, the skill had something to do with hardening your muscles. Which didn't really make sense, but it seemed to work for some reason.
Next Garp showed the boys the opposite skill to tekkai called, kami-e. It was a skill that gave the user extraordinary flexibility and allowed Garp to avoid any attacks the boys attempted on him. It gave his body a paper-like state, which looked a little funny to the boys at first. But after ten minutes of never being able to hit Garp, the boys admitted the skill would be useful. As for how to do it, the only thing the boys could think of currently was to become very flexible.
Afterwards Garp showed the boy's shigan, which was used as an attack. He used a single finger to poke a bunch of holes into a large boulder. He also used the skill on a tree before he showed the boys it could be used with different fingers. Once he was done with the demonstrations, the boys had a couple ideas on how the skill worked. But they would need to test things and narrow it down. One Idea Marcus had though was using tekkai on a finger to be able to use shigan. How they could harden their finger muscles in the first place was a whole nother story though.
Garp then showed the boys soru, which turned out to be a movement skill. All the boys really liked the skill because of how fast it could make you move and how it could be used while fighting. Again Garp only gave them some demonstrations and didn't explain how the skill worked. But the boys had a single solid theory on how it worked. You had to kick off the ground multiple times in a single second and it would make you move at incredible speeds. They only came up with that because they noticed how fast Garp's feet moved when he used the skill.
Rankyaku was the next skill Garp showed off where he kicked the air and made wind blades that cut large boulders and trees in half. Then Garp showed off the same skill using his arm and cut down a few more trees. This skill seemed easier to figure out just like geppo, since the attack was made using the air. Marcus shared with the others that Bogard showed him a similar skill using a sword and that it was a wind blade based attack also.
As for the last skill Garp showed off to the boys, it was called rokuogan and was pretty much crazy. Garp was able to shoot out a shock wave like attack from his fists that completely destroyed a tree. How it worked none of the boys could figure out and Garp only said you had to master all the other skills to even be able to use it. The boys decided not to worry about that skill for now and instead thought of different ways to practice the other skills.
After Garp showed off all the skills he asked, "So what do you think? Pretty awesome, just like your grandpa, right?"
The boys shared a look before they said, "Whatever you say grandpa."
Garp lifted a fist in the air as he said, "You little brats, let me give you the fist of love."
"Run! It's an angry gorilla!" Luffy said as he started to run away.
"I'm not a gorilla!" Garp said as he raised both arms over his head.
The other boys all laughed as they also tried to run away but Garp caught them all in a flash and gave each of them a large lump on their head. Afterwards he left to cook food as the boys went off to start their morning training. From that day on, the boys settled into their new training routine with Garp.
During their training Garp also took over gathering food for the boys each day. He specifically fed them different types of sea kings for every meal. Within that three month period all the boys had a growth spurt, as each one of them gained almost a foot in height. Marcus brought up the issue to Garp as he thought it was a little weird. It turns out Garp wasn't joking about sea king meat making you stronger, it also made a person's body grow larger then it should.
Marcus wasn't sure how much bigger he would get if he kept eating mostly seaking meat, but being a little taller never hurt. As it stood already, Luffy already looked a little older than when he was first introduced in the original story. His body was slightly bigger and he didn't look like a tiny kid anymore with the new growth spurt.
Ace and Sabo also looked different than their story counterparts. Both boys were noticeably taller and were already showing signs of visible muscle. Ace in particular was looking a lot more like a younger version of Roger then adult Ace in the manga. Hopefully it wouldn't affect him when he was older and make his pirate journey harder, but who knows.
And as for Marcus himself, while the right side of his face looked close to Luffys. The massive scar on the left side of his face, made him come off as overly serious all the time. Pair that with his sharp, purple colored eyes, and most people wouldn't realize that he and Luffy were related, let alone twins. Marcus also cut his black hair extremely short and was slightly bigger than Luffy from pushing himself harder in training.
Besides the training Garp had them do, Marcus worked on his sword mastery after dinner each day and any free time the boys had. He still needed to work on the sword skills his sword was teaching him, but a week after seeing Garp's display and chatting with his brothers a few times. He had a new goal in mind and something he wanted to learn. While Marcus already knew about rankyaku and the other secret arts Garp showed them from his past life. Something about seeing them in person, inspired Marcus to attempt something he already gave up on trying for now.
He took Garp's demonstration along with the one Bogard showed him over two years ago and started figuring out how to produce a flying slash. He had attempted it before, but it never worked out, no matter how many times he attempted it. Marcus originally thought it was because he just wasn't strong enough to produce the air blade and still couldn't cut down a tree with his blunt training sword. But now he had a different idea after watching Garp use rankyaku up close.
While the rankyaku skill did require a lot of strength to perform properly, the slash Bogard showed him was the exact opposite. When Marcus thought back on that time, Bogard looked like he barely put any effort into his attack, no extra strength, just a casual swing of his blade. Yet that blade produced an air slash that could slice a boulder in half from a distance. So Marcus focused on figuring out how to make an air slash that way.
It was slow going at first but about a month into his training, Eternal Rest seemed to understand what he was trying to do and readjusted his movements. Since his sword helped him a few times before at this point, Marcus was used to it and let the sword change his stance and swing over the next few weeks of practice. When the sword was finally satisfied with Marcus's progress, he felt a tinge of happiness from the blade and something else. It almost felt like the sword was proud of Marcus.
Afterwards Marcus practiced his new stance for over a month before he finally produced an air slash. The slash itself was nothing and barely flew a few inches before it disappeared. But Eternal Rest vibrated in his hands for his first successful slash and he could even feel joy radiating from the blade.
With the knowledge he could produce an air slash, Marcus redoubled his efforts with his practice. After another fifty swings or so Marcus produced another flying slash. While Marcus was happy with his progress, over the next week or so he realized he couldn't consistently do them. It took on average at least fifty or more swings before he could make a flying slash. While the slashes were getting bigger and traveling farther, it wasn't by much. The current record was about two feet long for the slash and about a foot in travel distance before it disappeared.
Marcus didn't share his new skill with anyone yet since it wasn't consistent and he didn't want the others pestering him to teach them how to do it. Since he wasn't sure if he could actually teach Ace and Sabo, since they didn't use swords. Other than working on learning how to produce a flying slash, Marcus also focused on trying to perfect his breathing technique.
His technique was supposed to work like total concentration breathing from demon slayer, but so far the only benefit his technique gave him was being less out of breath when doing physical activities. While nice, Marcus was hoping to gain the other benefits from it like increased strength, speed, stamina and endurance. It also increased a user's mental abilities to keep up with their super human movement.
His work on the breathing technique didn't really go how he wanted though. Whenever he tried to change it, it just felt wrong, even his sword would shake slightly to warn him. It left him with a few choices, either keep trying and hopefully figure it out one day. Start all over again and try to create a better breathing technique from the start. Or finally just give up on the breathing technique and be happy with what he already had.
After a couple days Marcus decided on pushing forward with his current technique but before he started trying to improve it again. He wanted to increase his lung capacity and currently didn't have access to any type of gourd so he started running more. Marcus also started doing suicide drills/shuttle runs in the clearing at the base. He set up ten sets of rocks twenty feet apart and would do them at least four times a day. Garp watched Marcus do them the first time Marcus set up the rocks and liked the exercise so much, he incorporated it into the boys normal training routine. So for the past two months all the boys were doing the exercise at least twice a day.
Garp also kept his promise and trained the boys to be able to clear all six training grounds by the two month mark. After that he focused on pushing the boys to complete the six timed training courses and getting on the leaderboards. While the boys were able to get on the leaderboards after a couple weeks of pushing themselves, they were near the bottom of the two hundred names posted.
When there was about a week of training left before they departed the island Garp said, "From here on out, you don't need to do your normal training. Your only goal is to make it within the top fifty of the leader boards on the timed obstacle courses."
"We can't even make it into the top one hundred on any of the boards. How are we going to make it into the top fifty?" Marcus asked.
Garp pointed at their training harnesses as he said, "You're going to run everything without the harness on."
Luffy jumped up and down as he said, "Without the harness I should be able to get first place on all the courses!"
Ace punched Luffy on the top of his head as he said, "In your dreams, I'll be the one in first place loser."
Luffy rubbed the top of his head as he said, "You'll be the loser when I beat you."
"You've never beaten me before, not even in card games." Ace said as he smirked at Luffy.
"I will this time, just wait!"
Garp laughed before he said, "Tell you what, whoever gets the best overall scores will get a prize the next time I visit."