*killua cackles at gon's muffled response, unable to understand a word of it but getting the jist -- he's on. killua lashes his muscular tail, cutting through the water with ease and gliding around the curved edge of the tank as gon chases after him. he glances over his shoulder, seeing his tail flash and glitter between him and gon, and grins.*

it's really not so hard to use, once you get the hang of it!