"Practice!"

Swimming on their backs isn't a bad idea at all, is it? So Tidus kicks up his legs, lets his head fall back, sighing at that weird sun hits his skin.

"I can teach you! You can learn on the train too, but you need to keep it up! A few minutes each day, and you'll learn to hold your breath longer and longer."

He says it like a challenge, but one with an obvious reward.