Just use advanced player. Master has a different meaning, it’s actually unfit to be used considering the plot and context (I’m an Indonesian native). Advanced player in Indonesian is too wordy, but the translator could have translated it as, for example, expert player rather than using the word master. I think it’s closer in meaning. Master is much more than just an expert or advanced, and it somehow implies that the character’s ability is not growing anymore, since it’s already on the top level. It’s the opposite of what’s happening in the manhwa.