At the end of the year, Umao-kun decided to spend his winter vacation at his grandpa's house in the countryside. At his grandpa's house, he meets Yui Yui. It's a shame that Yui Yui always spends her time in the countryside, so he decides to please her using his grandpa's tools. This is a masochistic drama about Umao-kun, a boy with a huge dick that rivals that of an adult, and his female body service!