I'm pretty sure it was a oneshot. It was set in a world where people would play this sport that involves racing with this sea creatures (I can't remember what they were. Maybe dolphins). A boy ends up spending time with one of these creatures so that he can race with her one day. Then one night she takes the form of a human. In the end they race and escape. That's all I can remember. It was kind of a weird story but I liked it, so I really hope someone can help me remember what it was called.

It is Over the Blue. =]