People who are concerned about underwater breathing and how they do it

You have a volleyball with razorblades that you can spin, and throw (without damaging yourself) and turn someone into stone

You have the ability to pay monsters so they leave the battle (bribe technique)

When members of the party have fainted, and there is a summon animation coming up, they unfaint, leave the area, then come back and conveniently refaint at their previous spot.

I think blitzball breathing is the least of the lore questions that need to be answered lol.