By charging up a RP, you get to activate a certain attribute that's given on your respective skill.
To adjust the attributes, go to the skill tab and click on the flower icon, this brings you up to an interface with all the avaliable attributes the RPed skill can perform.
To activate a RP skill, simply hold down the hotkey while having the effects preset. Effects can range from Damage multipliers, Knockdowns, EP cost reduction, etc.
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