Kairi dares Sora to be stupid. Sora, of course, complies. Riku/Sora if you squint.
Neither questioned Riku's gullibility, and so Sora waded into the water while Riku was changing. All the better that the older boy had beaten Sora in yet another race the night before. This would show him. He chose a patch of water that looked darker and more drown-worthy than most, letting his feet slip off the sand as it dipped deeper. Riku would take a minute, at most; Sora forced himself to take deep, rapid gulps of air, his head fuzzing with excess oxygen. On the beach, Kairi carelessly picked her sunburn and watched for the boy.
She jumped up as a silver-haired figure appeared, the signal. With one last heady gasp, Sora relaxed his legs and let himself sink. Kairi's voice was squeaky, and Riku turned sharply to the ocean. Sora let out a yell half-drowned in the water before dipping himself under completely. Wet haze overtook him, blanketing his eyes and stuffing his ears with a thick buzz. There was the flushing sound of displaced water, magnified in the way that noises will underwater. Sora grinned evilly to himself, then assumed the position agreed on by him and Kairi, the one most likely to scare Riku silly. He closed his eyes, opening his mouth in a slack O. Relaxing his arms, he sank down further; the pressure pushed into his ears and soft spots, but he forced himself to remain calm.
Riku got to him faster than Sora gave him credit for. Grabbing the younger boy under the armpit, Riku dragged Sora up to him, using his other arm to pull them flush against one another. Sora tried not to tense up or move away. Let it carry on for a little longer--
Riku did not wait to pull Sora above the surface. Sliding one hand to the nape of Sora's neck, his mouth collided solidly against the younger boy's, forcing warm air from his lungs to Sora's. Sora jerked, his chest swelling involuntarily with air. Memories of CPR lessons and rubber doll kisses flooded his mind. Riku was watching at him through slit eyes. They were dark and critical, watching the younger boy's tensing face...did his eyebrow just wiggle? Sora blanched as he felt Riku's body contract in an airless laugh; he hit the older boy on the chest and kicked himself free, grappling for the surface. Surprise had catalyzed the mortal panic he worked to suppress earlier, and he could feel the water beating in on him. He shot up, breaking the water with an agonized wail. Riku surfaced a moment later, coughing water out of his lungs. Kairi had abandoned her post on the beach and stood in the tide, her fingers raking at her burn.
"You jerk! I hate you!" Sora splashed water at Riku, who grinned and dunked the brunette.
"You thought you could best me? Are you /high?/" He taunted with amusement and the slightest bit of contempt. "I wasn't born yesterday, Sora."
"Yea, yea." Sora turned towards the shore, but the taller boy stopped him, catching him by the back of his trunks. Yanking him back, Riku leaned over and grinned in the feral way he did.
"I'm not done," He stated plainly, "you little bastard. You ever, ever do that again-"
Sora twisted his neck to look up at Riku defiantly. "And you'll what?"
"I'll let you fucking DROWN, that's what." He dunked Sora again, pushing past him towards the shore.