It had been ten years since that talk with his grandmother and he has stayed true to his word. The next day after the talk he headed up to the mountains as far as he could go. The first trip took him to the very bottom, where he started working out his 4 year old body. He had no idea what he was doing at the time so he just followed his instincts. He was thankful for his third wish as he would have never progressed past the first day. He started with small things he could do, such as sprints and footwork exercises. The more he trained, the more he progressed.
It started slowly, with things like changing his limbs for as long as possible before being exhausted and writing a barebones training plan. After getting the hang of transformation he started getting faster and faster until it was a 1 second delay. The next was to build his base form, he didn't want to rely on his transformation to be strong. Just thinking of the original kaido and zoro had given him a good idea of where to go. The benefit of having the dragon fruit also extended to his base form, he had remembered in the manga that kaido was basically indestructible and tried to replicate it with success. He started with studying medical books to see if his idea was even possible and it was, it would take 9 years for him to get it right but by the end of his training he was indestructible. The basic premise was this, 'what if I made my heart a dragon heart?' then inspiration hit him. He had read fairy tail and remembered acnologia who was a human turned dragon. What if he gradually changed his heart from a human to a dragon, pumping dragon blood into his veins? the answer was clear. You would slowly overtime become a dragon, but I didn't want to be in my dragon form so I basically overtime became a human with dragon cells in natural form.
This led to cellular level dragon scales covering me, giving me kaidos near invincibility. This also led to a passive strength gain over time, giving me incomprehensible strength. While this would take the better part of 9 years I also focused on the original zoro.
My father in this world had been an average swordsman but I wanted better. I hated the sword in the mouth of OG zoro so I went with 2 blades. I knew I couldn't cut people open so I used wooden swords all the time, eventually getting to nigh unbeatable with a blade. The only problem was that I had no opponents so my skills were not the best possible.
You might be wondering then 'Well what about haki', oh I trained that before anything else. Before even picking up a blade I had been hitting the mountain for years trying to get armament to awaken. It was going to be my most used skill in this world, so it had to be the best it could be. After awakening armament in my 4th year of training it only got better. My 3rd wish was possibly a little too overpowered, causing my potential in everything to skyrocket if I trained. I had haki flow by year 9 as well but it wasn't great, it destroyed to much instead of being deadly precise like I wanted.
Observation Haki was my worst and least used skill. I was about timeskip luffys level, but I didn't want to cross a 2 second time zone. I didn't want to look into the future that much as that would be boring and the longer you looked the more of a disadvantage you had because of the flow of battle will make you hesitant if you see to many options.
As for conqurers... I was able to coat my wooden swords in conqurers coating on the last day of training. I had unlocked it after gaining my zoan form which was a pain in the ass. I basically sat on the mountain during storms and hoped lightning struck. After the 13th time of hitting lightning with armament I began to feel amazing, I almost lost concious because of the energy that circulated through my entire being but forced myself to stay awake, I was so pissed off that I swung my sword as hard as I could putting everything drop of haki left into it. Releasing a scream so loud the air vibrated. I felt a lock breaking inside me before I suddenly bulked up, ripping through my clothes. I eventually stopped at 55 feet in size, barely holding on I felt as it i was a god in a world of cardboard. Roaring at the top of my lungs I passed out, unaware of the animals on the mountain dropping like flies, foaming at the mouth.
After some of the villagers finally came in search of me, they found me in my dragon form before I reverted. After finally seeing the results of my training I was finally finished. I took the next few months to relax, I had been training for ten years at that point and it almost made me Lose my mind obtaining all that strength from just being a regular human before my rebirth.
I had 2 years before to go before I would be 16. 3 years into my training and I realized that I wanted to see the world, I told Grandmother chio about this desire and she made me a deal. I could leave at 16 if I proved I could actually support myself financially.
Having 2 years till then seemed like a long time but I wanted to publish some manga before long. That's when I created a training schedule for my writing and drawing skills in the form of copying one piece from my memory.