Lol, Luffy didn't train his advCoC. He found out after getting hit by it. Only armament can be trained. Did you forget Luffy punching iron at Udon to learn ryou? Did you forget him not touching the tree to destory it?
Man, there always has been a trail for AdvCoC. Dont cope too much bro. You sounding like zolofans when they were yetting ZKK everyday.
Sigh. Why do people write and respond without articulating or actually taking the time to read?
THE ONLY HAKI TYPES THAT CAN BE TRAINED ARE ARMAMENT AMD OBSERVATION. I ALREADY STATED THIS. THE BATTLE SHIP BAG TRAINING THAT KOBY, AOKIJI AND KUZAN WENT THROUGH WAS NOT TRAINING ONES HAKI BUT INSTEAD WAS A TRAINNG BUILDING UP AN INDIVIDUALS BASE STRENGTH.
THE ONLY HAKI TYPE THAT CANNOT BE TRAINED IS CONQUERORS HAKI. THE ONLY WAY FOR COC TO INCREASE IS FOR THE INDIVIDUAL THEMSELF TO BECOME STRONG.
Koby didn't train up his haki hitting the battle ship bags since you aren't allowed to even use it for training lol.
The black trail example you spit is also false since we also see black trail emit when there is a clash of basic coc or even coa. So the black trail argument is mute.
The only way in which the black trail is used to coherently identify advanced coc is the black lighting itself emmting from the fist or weapon without clashing or hitting an object
Before kaido hit luffy with thunder bague we see the black lighting emit from his club. Before zoro hit king we saw black lighting emit from his blade. Before garp even threw a galaxy impact punch we saw black lighting emitting from his face. This is not the cade with regular coc or coa or even advanced coa. The only time those versions of haki have black lighting is when a clash is already made or when an object or person is already hit and not before hand.