After graduating from college and securing a job, Honoka moved to Tokyo to start living on her own. Until she finds an apartment, she stays at her brother's house, where she meets her sister-in-law, Yui. Yui quickly notices the hidden eroticism in Honoka and plots to turn her into her personal sex slave. Possessing an insatiable libido, Yui is a lustful demon—fierce and skilled with both hands—who gradually takes control of Honoka's mind.