Are you a new writer?? Or an experienced one. If you're new then maybe you can adhere to my ramblings.. This are the ff.
1. The MC personality is bland, make sure you have a proper lista of his certain characterstics whether if you want him to be eccentric, cold blooded, happy go lucky and etc. He just killed peoplr out of nowhere and did'nt even state his goals. Build proper character build up for other as well. Lists all the things you want them to turn into.
2. Some words are a mess, what the heck his "Counter Admiral", before posting the chapters, can you double check it to avoid errors. 3rd PoV's need to be worked also, some thoughts didnt match with each other.
3. Give proper information in your system. It was not porperly discussed at all. The techniques you made didn't even make sense, is a training a technique that needed for the system to recognized? Nope it is not, it is just a process in which people will do repititive tasks to enhance their body. Add skills also to the MC, don't give broad skills and be specific about it.
Lastly the most important one, since you gave him instant mastery, why the hell he needed training for??? He can just use his knowledge in the anime to do the techniques step by step. Like physical exercise, do the running (insantly mastered it), do push ups( instamt mastered it),
do meditation (instant mastered it), Do blindfold and evade projectiles( awakened his perception (intant mastered it) and evolved it to (Observation Haki)..
You made your fanfic and its core is Instant Mastery, which means the MC can basically master everything instantly.
Please be reminded, maybe you can create (Power rankings in your story whether if it is techniques, skills, marine levels, pirate levels)
Such as
Low tier, Mid tier, High Tier and etc. in order for your story to be fascinating and be executed well..
