After the conflict between the Shandians and Skypieans was settled, the Straw Hat crew left to conquer the rest of the sky island for their empire. There was one problem though, the other islanders were really weak. Due to growing in a basically self-sustaining environment with no conflicts with the other faraway island, the islanders grew with no conflict or war to shape them like the citizens of the blue sea. Skypiea was the most advanced due to the war with the Shandians and Enel's interference, but the others were pathetically weak.
"This... Is a massive disappointment." Luffy said after they claimed 12 sky island as their territory. "We definitely need to train them, otherwise they will not be worth the effort," Law said and everyone nodded with agreement. "They have potential, but we can't just go island to island. We need to train them, and then let them go train the others. That way we'll gain new forces even without doing nothing, and the amount will only continue to increase as new sky islands are discovered." Luffy came up with an idea.
"But will they be willing to bow down to us? Up until now, we showed them the disparity between our strength and theirs, and that's why they agreed to be part of our territory. But if a group of Skypieans comes to another island after we trained them, unless the gap in strength is absolute like ours, the island won't see us fit to command them. It is possible, but it will take a lot of time." Katakuri explained.
"Don't worry, we have time. Besides, the level of the Sky Islands isn't that low, so it shouldn't take long at all to train the Skypieans to a good enough level. Also, besides you, the rest are still too weak to build a good base for our empire. I have more crew members in mind, of course, but they either have enough strength already, or they don't specialize in combat. In short, these two years will be used to train both the Skypieans and ourselves, and scout more members that will join our crew," Luffy said.
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The Straw Hats spent the next two years at Skypiea, training themselves as well as the Skypieans and Shandians. Luffy and Katakuri were the ones training the groups. Luffy had the role of training the crew and the rest in combat in all sorts of scenarios, as well as assisting them in special cases like guiding Zoro, Brook, and Law in their unique sword training, as well as Sanji's leg style and Nami's staff fighting. Katakuri focused more on training them and the rest Haki, with special care on Usopp as he was a sniper, and would profit greatly from his Observation Haki techniques. Robin trained almost exclusively in Haki since that made a devastating combo with her Devil fruit.
The Skypieans and Shandians were advancing at a marvelous speed as well, with them focusing mostly on Haki. At some point, just to test them, Luffy sent a group of Skypieans to a near sky island to see if they manage to recruit the inhabitants. Long story short, it was a huge success. The Natives there were no match for the small group of Skypieans, and after stories of the dangerous blue sea inhabitants, and their emperor who taught them, the island agreed to become the Straw Hats' territory for the benefits that were offered.
and so the Islands joined, trained, sent an envoy of their own, and repeat. All the while, the Straw Hats were training themselves. But the Straw Hats' sudden disappearance didn't go unnoticed.
No one believed that they died, since how could one of the emperors die with not even news of the battle, so most of the high-level players assumed that the Straw Hats are working on something in secret.
The Underworld launched countless search parties to find Luffy, as they did not want to anger him by trespassing on whatever territory he secretly claimed during his absence, and also to form friendly relationships with him as he was still a neutral force to the Underworld.
As for the other emperors, they didn't worry much, except Big Mom. Shanks and Whitebeard had very friendly relationships with Luffy, so they didn't bother looking as they knew he was alright. But Big Mom was different. After the humiliation, Kaido, now known as Buddy, suffered she was outraged. She demanded Luffy's head and tried to contact Katakuri to tell him to kill Luffy. Unfortunately for her, Katakuri didn't take his Den Den Mushi when he first joined Luffy, so she had no means of contacting him. But even though she had the mentality of a child, she realized that she had no option but to take her time and plan Luffy's demise.
The World Government was especially panicking, since having an emperor disappear to somewhere even they don't know gave them a heart attack. They searched madly to find Luffy's whereabouts, but they found nothing.
Some speculated that the Straw Hats found an ancient weapon, and were planning a war. Some thought he joined the revolutionary army since only they worked in such secrecy. Whatever the case was, talks about the missing emperor slowly died out during the years, leaving only the important people frantically looking for him.
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*2 years later*
"Alright, I think this is enough for now," Luffy said as he looked at the masses standing before him. In those two years, the envoy plan worked like a charm, adding countless islands to the Straw Hat empire. Although each island didn't have a lot of residents, they made quite the force when combined. Over these two years, over 100,000 Sky People joined them, and more were always recruited. Moreover, the level of the normal soldier was that of a Marine Captain thanks to the intensive training they received, and the fact that all their training was done will a minuscule amount of oxygen as a result of their current height.
As for the crew members, needless to say, that they skyrocketed in terms of power. All of them easily taking on a Marine Vice Admiral, and most of the combat-oriented ones nearing admiral level.
"We have been gone long enough in the Blue Sea, I want to see their reaction as we build our empire right in front of them. And now that we have the ability to fully crush our opponents, let the fun begin" Luffy declared in an overly dramatic fasion.
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Nothing to rant about today, except some BS levels of homework, though I'll rant about it another time. Hope you enjoied.