Byleth splashes into the water, apparently deciding that the best way to acclimatize to the temperature is to just rip off the bandage and jump right in. There are some merits to the shock approach, perhaps. When he surfaces again, his hair is plastered down onto his face and he has to swipe at it to clear his eyes. It's an endearing thing.

Dedue enters the pool at a much more sedate rate, stepping in until the water reaches his hips. He'll have to go quite far before the water reaches anywhere high on him, but that's fine.

"It is quite pleasant," he replies. "Please be careful, though. You will burn more quickly in the water."

Because Byleth is about as tan as white bread. Dedue, of course, will have no issues with the increasingly intense sunlight, but the dragon pope has no such defenses.