Mastery, also known as Proficiency, is an intricate leveling system for Special Arts and Symbology in the Star Ocean series. It allows these skills to grow and improve over time through steady usage, increasing their effectiveness or even changing the execution of the ability entirely.
A Mastery counter is not actually visible in Star Ocean, but the usage of Special Arts is recorded. Special Arts that correspond to stronger arts within Secret Fighting Techniques must first be "mastered" through a number of uses before the new technique can be learned in combat.
Known as Proficiency in The Second Story, most Special Arts and Symbology record uses up to 999 times. Most individual abilities have their own 'level' of proficiency points before they improve one or multiple times; the amount of uses to improve each art and spell vary.