>>532171665
Seia recovers cost with her EX buff, she also halves the target student's EX twice at level 5. So as long as you're using it on a skill that costs 2+, you're gaining cost, all while cycling back to your DPS.

>>531168385

>>530531565
It's equivalent to having another student in the team.
Here is the exact cost she gives based on whether UE40 or not and/or with cost recovery specials.