An older brother succumbs to the provocative temptations of his younger sister Yuna, who has secretly been in love with him since they were little, and takes the plunge into forbidden incest. With her long-awaited desire fulfilled, the younger sister begins asking for sex almost every day. And today, her parents are once again out late into the night. The moment their parents leave, Yuna seeks her older brother. "Let's have sex all day today, ok? Big brother?"