sorry i didnt get it, how did he become the master.? im confused..

As far as i understand it (but not really sure)
When someone has learn about the ghost technique something (when the MC tried to find the way in to the ghost village) he/she will become the new master of those ghost and the previous one has left or died or idk where..

because that martial art that he learned so he could cross the illusion was the martial art that only the master of ghosts knows(it was hidden in the poison valley 300 years ago by the first=previous=the only master of the ghoasts so far). so by knowing that art he was recognized as their new master.

hope it helps, that's as far as I get it ╮(￣▽￣)╭

thanks guys, now i understand haha i reread it but didnt put two and two together xD thanks again..

It's the martial art of the famous thief