25-year-old Daon had a dream. Having a fantastic and beautiful first experience! She even saw the size that would make for a fantastic first experience. The problem is… The person with that size is her brother’s friend, Na Woo-hyun! Na Woo-hyun, who has been coming to their house since they were young, is her brother's friend, nothing more and nothing less! Gaon keep telling herself not to have such feelings, but even when she close or open her eyes, the size of Na Woo-hyun keeps coming to her mind! Gaon went to the extent of trying it with her ex-boyfriend but was extremely disappointed with how small it was! In the end, Daon couldn't miss the opportunity- ❝Brother, sleep with me just once.❞