He dives into the cold valley water without hesitation and splashes water at Natsuki, who was spreading out a mat.

Too slow.

After getting drenched while setting up the mat, he rummages through his bags, pulls out a custom-made water gun, and retaliates against Gaku.

Pushed back by Natsuki's water gun, Gaku uses brute force to lift Natsuki up and hurls him into the valley water.