Takeru Daigo is a boy living in Tokyo who doesn't like milk. During summer vacation, he decides to go to Ushiojima by himself to visit his grandmother Tomi. To his surprise, there is a talking milk carton named Kevin in her refrigerator. Kevin encourages Takeru to drink milk, but he refuses. Along with the help of his other milk friends who live on the island, Kevin makes it his mission to get Takeru to drink milk!

(Source: Official site, translated)