Tennis no Ouji-sama: Message in a Bottle
テニスの王子様 OVA FAN DISC ～Message in a bottle～
Picture drama episode included with Prince of Tennis official DVD fandisc.
Atobe, sneakily, throws a message in a bottle in the river, which winds up next to the Rikkai and the Seigaku regulars.
(Source: Prince of Tennnis Wiki)