Jun, who just got a boyfriend, feels insecure about her sexual skills and asks her older brother—me—to help her practice. She tries various blowjob techniques she researched online, but as she does, her brother gradually finds himself drawn into the experience. What started as mere practice slowly evolves as both begin to develop real feelings, deepening their bond step by step. Soon, the special connection forming between them begins to pull Jun in far more powerfully than her relationship with her boyfriend ever could.