Suddenly, two close sisters were born after their parents remarried. However, the two sisters are secretly conducting forbidden research...! The two sisters are so greedy for sex that they are super perverted sisters who conduct research on sex every day. They search for each other's pleasurable spots and use vibrators and rotors to research what feels good! However, one day, after peeking into a secret research group, the sisters' interest turns to their brother's dick! They say they want to feel good with his dick! Of course, there's no reason to refuse!