You have a little sister who is always disrespectful to you. This little sister is really a bad kid but she has another secret. With the help of the devil’s power, this little sister becomes even more unruly and domineering. However, you are also lucky to have a power that can break into sleep; to be more precise, you can put others to sleep and hypnotize them. Imouto Darkness will be the journey where the player teaches his unruly little sister and uses the power that a devil has given him.