A word from her brother transformed her plain sister, who used to go to school without makeup. She treasured those words and improved herself. She was happy when her brother called her "beautiful." However, her brother couldn't resist and tried to cross the line between siblings. The sister proposed a promise to only do "sumata" (intercrural sex). This created a wall. However, when she thought about her brother, her heart ached. Even though she tried to control herself with reason, she wanted to touch his skin... "Not just sumata, but also penetration..."