The younger brother, frustrated by being constantly ridiculed for his virginity, decides to take revenge on his sister. 'There's no way I'm going to cum for you!' the sister had boasted, but when the brother suddenly pulls out an electric massager, she responds with 'I wasn't told about that...' and ends up climaxing repeatedly. Eventually, unable to hold back any longer, the brother inserts his virgin penis into his sister's vagina, committing incestuous taboo sex for his first time.
