Iris Yuma Skill : Burst

when you use the skill, your FIRST HIT damage (no matter what hit) is enhanced. (it's the same thing on JP/KR version)

Like if you do a skill with multi hit, ONLY the first hit is enhanced

It's only "good" when combined with such skills as Hail of Plasma or Plasma Portal and maybe with initial hit with Fire Spin because of highest damage per hit. But yeah it looks pretty strange in her kit where almost every skill is multihit and only Hail of Plasma can be turned to single strike with Meteor extension And Burst is second the most SF consuming(60 SF) skill after Plasma Portal(75 SF).

Not to mention that some FS puddle or Eternal Abyss will gladly eat this buff regardless of your plans on using it with something else

Well it may be not so useful for Iris but it still a party buff so maybe it can be handy for other characters.