Jack is in Marineford. He was not promoted as he just joined marines. Jack didn't mind as his focus is now on increasing his power.
He wanted to learn advanced haki as soon as possible. He need a partner or someone who know this. Z don't want to teach him saying that he is busy. Jack felt like he is avoiding him.
All those who Jack can ask are busy with their work. Only one was carefree ; he went to vice admiral Garp for learning it. " You want to learn that, why ? ", he asked for a reason.
" To get strong ", Jack. Garp laughed at his answer. He asked why he wanted to be strong. Seeing that Jack was silent , he didn't asked him again.
" Come with me ", Garp took him to a nearby island. It seems like a man made island for fighting. Garp gestured him to start.
Jack got behind Garp for sneak attack. Before his attack could connect, his mind went blank. " Sorry, I don't like sneak attacks. I got serious for a moment ", Garp was laughing at Jack.
Jack was shocked to the core. He know his strength, he can fight with admirals for few minutes at best. I really need to get strong, thought Jack.
Garp was laughing all the time. He is thinking Jack is genius. When Garp punched him on face, he used full strength to hit. Jack couldn't dodge but hardened his head on instinct. Garp was astonished by it.
Jack didn't know it but again got up for another round. Garp was only using half of his strength for Jack to adapt.
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Garp and Jack are eating lunch ; " Can you explain about advanced armament haki ? ", Jack asked him. Garp stopped eating and asked him.
" Show me your haki : hardened ", Jack showed him. " When did you started learning ? ", Jack told him 3 years. " It is nothing ; you just need to emit haki outside ", Garp explained to him.
" Can you show it to me ? ", Garp stood and walked to a wall. He placed his hand on the wall and used it. The wall got cracks and turned into pieces. " Do you get it ? ", Jack nodded.
" Shall we start ", Garp cracked his knuckles ; this will be going for a while, Jack thought and took beatings.
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" Garp, are you training him ? ", Sengoku asked after few days when both took a day off. " He asked me to teach. I can get rid of some stress by beating him ", Garp laughed at him.
" Don't you think he is getting stronger fast ? ", Sengoku is serious. Garp stopped laughing , "He only learned haki for 3 years but his control and strength is like a 10 years user ".
" Do you think he has it ? ", Sengoku asked him. " I didn't ask him. May be he can use it ", Garp sighed. If he can use it, I don't think he can be a marine , Garp thought.
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Three months have passed since Jack started fighting with Garp. He is able to fight for a while when Garp is using half of his strength. Jack is using his devil fruit for speed.
" Can you use Conqueror's Haki ? ", Garp asked him when they finished meal. " I can; but I can't control it ", Jack's answer shocked Garp. Even after using haki efficiently he cannot control it ; how high it is, Garp thought.
" Use it now ", Garp in a grave tone. Jack used a it for a second and stopped it. Cracks formed on the table and rest of the soldiers were unconscious.
Even Garp got dizzy for a moment. He turn his head to see his right hand man shivering due to it. Seeing Jack calm, Garp thought like he saw this situation in his youth.
" Hey, kid. Don't let others know about it ", Garp warned him. Jack sighed in relief. He took a gamble right now ; garp is a marine hero first than a grandfather and he is in his prime.
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" You are now getting used to my strength ", Garp. Getting injured daily ; his ability to restore made his body withstand to Garp strength. Now he is using more than half power to beat Jack.
" Now, you need to increase it more and start advanced armament haki ", Garp. Jack stops for a while and start his attacks.
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Jack got promoted after 5 months. He is now a Rear Admiral and appointed as a base commander. The previous one seemed to be injured ; he need to do the job temporarily.
" Why did you give him this area ; what if he quit the job ? ", Garp asked Sengoku. After 5 months of beating session Garp got more friendly with Jack. After seeing that area Garp thinks that Jack might quit marines.
" This is also a reason for me to do it. We can restrain him if he betrays us now. It will be hard if he grow more ", Sengoku said in a justified tone.
Jack know why he appointed him as commander in that area. He also thinking of doing the same as Sengoku said after getting more strength.