[ Katsuki's voice in Izuku's body is going to be absolutely ridiculous - but maybe there's another lost firefly, too? Izuku has more than one Quirk, but Katsuki only has the one. Izuku's still a merman this time around, and so he's simply swimming along the surface of the water and reaching up with tentacles or Blackwhip or both to try to snatch at the little balls of light to find the things he' lost. Take your pick: a soft, firm voice that isn't meant to be used the way Katsuki uses his, or one of the many portions of One For All, some of which are more difficult to control than others.
The splash of his swimming is muted in the water, but he's not really going for stealth right this second. ]
lost souls
The splash of his swimming is muted in the water, but he's not really going for stealth right this second. ]