Jon start his Haki training, his first training is Observation Haki. He is not succeed at all in a week, and only coincidentally avoid Koala's attack some time. It's not as easy as he thought, even if though spiritual energy is a part of chakra.
He find out that spirit actually have forms and abilities, that are used as Haki. Spirit have intent, presence, or will, that used as the source of Observation Haki. He need to feel that intent or presence of other's spirit using his own spirit. It's hard to do because intent and presence are vague concept that can't be grasped easily.
Spirit can be manifested in physical form, that is Armament Haki. Basic manifestation can't be seen, but as it got stronger, the spirit can be seen in dark colour. It can touch logia and hurt paramecia because spirit can also touch spirit. That's why with Haki, someone can touch devil fruit user's real body.
It can also be used as armour, because the spirit is actually strong. Spirit is basically a person's will, so if he want his spirit to be tough, then it will be tough. The stronger one's spirit, the stronger their Haki will be, especially Armament.
For Conqueror Haki, he assumed that someone need to have a very high will power. But Dragon said that Conqueror Haki is power that proof that someone have the will to be on top of others. In other words, a strong will to be a Conqueror, to be a King. It is a proof that someone have a quality to be a King.
Conqueror Haki is unique, because the ones that have it, are born with it. It can't be attain through any kind of training. Dragon have said that Jon have it, so he must be born with it. The most obvious trait of someone with Conqueror Haki is that he/she have a strong will that make him to never surrender to anyone and give up their goal.
'Maybe the God of Reincarnation give me this Conqueror Haki to make my mission easier. Well, i never use it before i get the nine tailed fox devil fruit. I never use it before right?'-Jon
"There are no Conqueror Haki users in Marines, because they surrender to WG and the rules of others. Pirates are a bunch of free people that didn't follow rules, that's why Conquerors can be found on them. You have Conqueror, so i guess you're not that obedient to your captain."-Dragon
"Oioi old man, don't accuse me like that! I always follow Captain's orders you know."-Jon
"Following Captain's orders didn't mean you are obedient, isn't that right, Miss?"-Dragon
"Yes, that's right."-Robin
Suddenly Robin appear behind Jon and he is surprised by this, but he's happy to meet her again.
"Our ninja here act like the Captain's big brother and often scold him or lecturing him. He even manipulate Captain's mind sometime, hihihi."-Robin giggle and Jon have sour look
"Oi Robin, we just meet after a few week. You didn't say hello but badmouthing me instead."-Jon have a wronged look.
"Ara, but that's a fact isn't it?"-Robin
"That's...."-Jon
Jon can't refute to that, he often teach Luffy how to act like a Captain and even scold him many times. It's usual in their crew, but Jon always act like a big brother to the younger members, including Nami even tough she is older than him. But that's only in this world, if he's not become younger, than he will be 24 y.o now, while Nami is 19, so she's younger.
The most obvious things that Jon did was that he never give up to anything that he decide. He will not listen to anyone, not even Luffy when he has decide what he will do. Like when he stay to fight Aokiji, or even when he destroy Buster Call, or even went to Impel Down with his battered body.
"Hihihi, i'm joking, altough it's a fact. Long time no see, little brother."-Robin
Jon widen his eyes hearing Robin call him little brother. He always think of the crew as his family, but when she call him little brother, he feel very happy. It feels like they are really a family. Unknown to him, he have tears flowing down, it's such a long time since someone call him brother, altough usually it's big brother, but it's same for him, it only used by a family.
Robin is surprised, but then she smile and hug him. Altough now Jon is taller than her, but she pull his head to her shoulder. Jon surprised, but he is happy and he hug her back.
"Long time no see, big sis."-Jon
Dragon and the others leave both of them alone. They must have many things to talk right now. The training can be done another day afterall. Jon & Robin stop after sometime and sit in a nearby rock's shadow.
"I want to ask your condition after you join the war, but it seem you're fine. You even look better than before, and grow taller so suddenly."-Robin
"Well, when i got injured so badly after the war, i get a surgery from Trafalgar Law. It seem to trigger some kind of dormant power in my body. My body actually change, you can think of it like a caterpillar that turned into a butterfly. I have a similar situation with that, heck, i even sleep in a cocoon when my body changed."-Jon
"So your body is evolving?"-Robin
"In a sense, yeah. Altough it didn't make me stronger instantly, i think now i have more growth potential than before."-Jon
"That is amazing, you can grow faster and maybe you can even surpass everyone in the crew when we meet again."-Robin
"I don't know about that, you should know everyone's progress since we sail together. It's not even half a year, and we are a lot stronger than when we arrive in Alabasta to defeat Crocodile."-Jon
"Well, that's true, especially you, Luffy, Zoro and Sanji. Now i can't imagine how strong the 4 of you will be after 2 years."-Robin
"Don't worry, you will also grow stronger. I will help you with that."-Jon
Jon & Robin then talk about what happen in these few weeks after they got separated. Jon also tell Robin that Kuma is a member of Revolutionary Army. They have attacked a Tenryubito, and most likely will be executed if they're being captured. So it can be said that Kuma saved them from being captured by Kizaru.
What make Jon sure of it was because Rayleigh told Jon that he have some talk with Kuma after Kizaru left. Rayleigh can even know Luffy's location even when no one else knew. Only Kuma can tell where he send Luffy with his power, so Jon sure that Kuma want to help them.
"If we got captured, i can only think that Luffy is the only one that can avoid being executed, Garp's influence is very big. The one that will suffer the most after being captured is you, the WG really want you afterall."-Jon
"Then we are in Kuma's debt, a very big debt."-Robin
"Yeah, but Kuma has gone."-Jon
"What do you mean?"-Robin
"In the war, i met with him again. Now he is just a mindless machine with no human emotion at all. He sacrifice his body to be used as experiment subject, that's why there are so many of those Pacifistas.He did that to got information that hidden deep in Goverment's body."-Jon
Jon already gave the Pacifista's body that they defeat in Sabaody to Dragon. It's what Kuma did for his friends in RA, so Jon will give it back to them to repay a little of the crew's debt to Kuma. He know RA have great scientist too, altough not at Vegapunk level, but there must be someone near that level.
Robin also approve Jon's decision to give Pacifista's body to RA. It was for Franky at first, but they don't even know where Franky is right now. So it will be better if they give it to RA, they can ask for the data and give it to Franky after 2 years. Beside, they're sure that Franky will find a way to be stronger even if he didn't have the remains.
"Did you still have your Rokushiki manual?"-Jon
"Yes, i keep it all the time."-Robin
"Good, Luffy almost lost it afterall. Luckily the girls didn't throw it away or misuse it. But it's also lucky that they take it from Luffy. He will lose it in either Impel Down or Marineford afterall."-Jon
"Maiden Island is it? I thought it's only a legend, but to think it's actually the base of Kuja Pirate. No wonder they only have woman as members."-Robin
They talk for some hours until it's finally the dinner time. They go to the dining hall and it was filled with people already. They go to the front seat and sit down. The food has been prepared too and it seem to be a banquet. It seem to be a celebration for Robin's arrival. Dragon stand up and Jon know it will be a boring speech.
"*ehem ehem* Attention! Today we finally get a special guest that we have search for many years. It's none other than-"-Dragon
Suddenly Jon slam his table and hold his mug. He gather everyone attention instantly and he smile.
"CUT THE CRAP OLD MAN! DEGENERATES, LET'S CHEER FOR MY SISTER, ROBIN'S ARRIVAL! CHEERS!"-Jon
"CHEEEERS!"-Everyone
They get into party in no time and leave their usual stiff personality. They laugh, sing, dance, drink, eat, and talk to people merrily. The only one that has a dark face is Dragon, it never felt good to have someone cut your speech. But he finally stop and sigh, then he look at his mens.
"Maybe i need to soften up sometimes."-Dragon
"Yeah, changing the mood sometime will be a better choice."-Robin
"Nico Robin, i'm glad you want to come and help us. I know that it's only because Luffy give you guys time to train, that brat told me about it. Even then, i really appreciate it, with your help, we will be a step closer to our goal."-Dragon
"Can you really do it? World Goverment has been standing for 800 years and no one can shake them until today."-Robin
"We can do it, we believe we can, and we must succeed. The way this world run right now is very wrong. It's running to a wrong direction and didn't get corrected in many centuries."-Dragon
"As you know, i only want to learn history. So i have no obligation to help you except learning history. My captain is still Luffy and i only follow his order, even now."-Robin
"Don't worry about it, i will only give you task that have connection with history and about poneglyph. We have found some poneglyph in some islands, i assume you haven't search every island in Blues and Paradise."-Dragon
"Of course, i'm only one person afterall."-Robin
"We have found some in islands accross these seas. We also make the copies, but we are sure that we haven't find everything."-Dragon
"So you want me to help you find these poneglyphs too?"-Robin
"Yeah, i know some poneglyphs are pointing to each other locations, so i just need you to read the copy. But if you want to follow the exploration, that is fine too."-Dragon
Dragon & Robin talk about these historical things, while everyone else are partying. They even forget about their reason for party, Robin who didn't follow their celebration. These guys have turned from their serious self to their easy going self everytime they have dinner after Jon come.
"This is how a dinner should be. ISN'T THAT RIGHT YOU BASTARDS?"-Jon
"YEAH!"-Everyone
They have party until they got wasted again.