I was reading up on the ItJustWorks Library and when they mention Junko's confusing Sub, that reminded me of her Basic being confusing as well.
It says "decreases the user's EX Skill Cost by up to 4", but it basically always drops it down to 1. They probably worded it like that to account for cost reducers, but just saying "reduces EX Cost to 1" would be less ambiguous.