From their shower, Luffy and the others brought him to their bedroom to a secluded room upstairs. When the three of them had their head hit the floor, they soon fell asleep without another word. Luffy was the fastest to fall asleep.
And he also fell asleep soon after, in this mountain, there was the sound of the wind blowing on the trees outside. It produced a whistling noise like a lullaby that lured him off to the land of dreams.
In a day where life seems to be speeding past at the speed of light, the moment of sleep is the only time without worries or fears. And the stars glistened outside in the night sky under a full moon with startling beauty.
The next day in the forest, Leo teaches the three how to train to be better. He said to the three of them, "In the world out there, you three won't even last a single day. So to get stronger, a firm foundation is needed right now."
"Won't even last a day?" Sabo repeated what he said in the form of a question to himself. His expression expresses his internal contemplation.
The three were sitting on the ground while listening to what Leo was saying. And he continued speaking to them, "To survive, you need to be stronger. Strength will give you the power to protect yourself. You three will be battling with me to train your ability to fight. Now stand up!"
Standing up from the ground, the three looked at each other and seemed to be giving each other signals through eye contact.
Without hesitation, the three started their attacks on Leo while he effortlessly moved away from their punches and kicks.
He grabbed onto Luffy's fist and made Luffy spin in the mid-air while giving a kick to Sabo and Ace, who were behind, causing them all to fall to the ground.
The separation between their skill levels was enormous, as they all stood up again while training to hold the pain.
"How are you so strong?" Sabo asked while holding onto his chest. The kick that landed on his chest blew him away. He had never experienced such a quick defeat.
"Even the opponents we went against before were no match for us," Ace commented as he regained his composure.
"Ace, Sabo, Luffy, the world out there is bigger than you can think," Leo said to them with a face of seriousness. "You know, in the New World, there are the Four Emperors, who have an army of fighters that can trample any one of you here effortlessly."
Hearing this, all three of them started to have severe faces as they listened to what Leo was saying. Then, he picked up a small stick that was sharp at the end, "And in the New World, a lot of fighters know how to use Haki."
In front of their eyes, something magical seemed to have occurred to the stick, and they watched it turn into a dark color. Luffy remembered this when Leo drew an X for him in the woods, saying, "I remember you were doing this before when you trained me."
"You three come and attack me right now," Leo commanded them. Sabo and Ace looked at each other before rushing to attack Leo from the front. This time they were more sneaky and made sure to spot some leak holes in his defense.
They watch as Leo easily dodges their attacks with his eyes closed. It was like he had eyes on the back of his head. He was moving and shifting his body in directions like a fish in water, "How is this possible??! He can still notice all our movements even with his eyes closed!?"
As Luffy's punch approached his face, Leo shifted his head away to dodge it just as it was about to hit him. Then, lifting his leg in the air to block the kick, the Sabo launched towards him from the side.
"What I'm using right now is called Observation Haki," Leo said to the three of them with his eyes still shut—moving his body and waist to shift in motion from Luffy's fist from the air. "It is a form of Haki that grants the user a sixth sense that allows them to sense the presence, strength, and emotions of others, as well as gain limited precognitive abilities."
"You mean they see into the future?!" Ace asked as he threw over a dozen punches from behind, which Leo quickly escaped from and kicked him away lightly in the stomach.
"Wouldn't that make the opponent near-invincible?" Ace stood back up from the floor. He was clutching his stomach. He couldn't even imagine what it would be like to fight someone who could avoid his every attack and create a counterattack.
"They are not invincible, but advanced Observation Haki will allow you to see a few seconds into the future," Leo commented as he stood before the three of them in the middle. "But you won't win with Observation Haki alone. It gives you 'information,' but you will need to arm yourself with the power to use it to your advantage."
He brought the stick to his face in an instant and opened his eyes again. They observe as Leo walks closer to a mountain that stands ten times his height. They saw how his arms seemed to turn a dark metallic color.
The air around his fist became steam with a single punch as the mountain pulverized into small blocks from that pressure. Then, finally, he turned around and said to them, "And that is Armament Haki. It hardens your body. It is usually used to make your punches harder or to block attacks."
By now, all three seemed to have turned into stones as they didn't even know how to respond anymore. The demonstration left them speechless.
"In the New World, there are countless devil fruit users, which grants the user supernatural powers," Leo says. Sabo and Ace looked at Luffy. Seeing their glances, Luffy smiled back at them playfully. "But there are also logia devil fruit users that can turn their body into ice or smoke. It would be impossible for you to defeat them without learning to use Haki."