All of Tsuna's friends show up at school during winter to help him babysit I-pin and Lambo. Although, in a turn of events, everyone besides Tsuna seems to just want to have a snowball fight, so Reborn turns it into another one of his staged competitions.

Tsuna has to swim 15m in school, but being unable to swim, he is trained by Yamamoto, Gokudera and Haru in the public pool. Everyone has his own method, and they decide to compete to see who can get Tsuna to swim the furthest. Reborn interferes this time with a Vongola dolphin that has a dangerous complexion.