Well first, we shouldn't start at this end of the pool. [He gestured to the 8 foot watery depths that had so intimidated Gintoki.] The front of the pool is much more shallow, so you can acclimate yourself to the water.

[With this, Katsura is pushing Gintoki towards the shallow end, not giving the boy time to protest or resist. They didn't have much time of gym left for all this hesitation.

He's even kind enough to stop his pushing at the ladder that leads into the water, though Katsura himself just slides in from the edge. He looks up at his friend.]

It'll be cold, but you're body will get used to it. I'll teach you how to swim on this end. That's why you've been hesitating, isn't it?

[An his voice is low, actually trying to help keep Gintoki's secret secret?]