A word from her brother changed her plain sister who goes to school without makeup. The sister cherished those words and polished herself. She was happy when her brother said "Beautiful." However, the brother couldn't resist and tried to cross the line between siblings. The sister proposed a promise of "only dry humping." Thus, a wall was built. However, when she thought of her brother, her chest became heavy. Even if she suppressed it with reason, she wanted to be skin-to-skin with her brother... "Not just dry humping, I want to insert." Before she knew it, the words came out. She couldn't take the step alone. But when she's with her brother, she gains courage. I want to be together forever and want you to watch. Accepting her sister's wish, the brother answered with a kiss.