Momo didn't think he'd meant to splash her- it was probably just an accident. Still, there was only one way to respond: with an all out attack. "Sparkling.. wave!" she shrieked, cupping her palms in the water and splashing it back at Seto. He was so startled by her naming her attack that he didn't even try to block it, and the water splashed him right in the face.
For a second he blinked at her, water dripping from his bangs and off the tip of his nose, and Momo thought she might have made a mistake. Sure, he was pretty easy going, but anyone might be mad if you got water in their eyes. Maybe she should apologize...
Before she could say anything though, a grin spread across his face, and he lunged for her, pulling her beneath the surface with him with a loud laugh that cut off abruptly as they plunged underwater. It was several long seconds before the two of them resurfaced again, blowing wet hair off their foreheads. As she caught her breath she could hear him laughing, and finally he called out, "That was my special submarine attack! Whatcha got to top it?" Momo narrowed her eyes with a smile. The game was on.