I think they did the quest with the intent to get a new shipgirl. Instead they got a desert as part of a pun and lightning just smiling at them saying "nice try, but you'll have to do much more than that if you want her."
They finished their first quest, but they weren't done with the entire questline yet. The last quest requirement within the chain was to have 30 fish in their inventory. Ikazuchi exchanged all their fish for Irako, so they have to start over from square one.
"It's fine for you to try harder, y'know!!"
Edit: I was wrong. The Irako was a quest reward.
She just wants everyone to try harder to get all 30 fish.
That's amazing, Commander!I have prepared rewards for you. Please take it, okay?...How 'bout that. I finally finished it, Ikazuchi.It was quite tiresome midway though. But with these, it's now completed!This is the first time I felt the terror from her smile.
