"Please… I just need a mouthful." For fourteen years, Gayoon had existed as a little sister to Taejun, until she inadvertently revealed something unimaginable. "Just give me a mouthful, and I’ll stop. I’ll forget about it." Throughout the entire fourteen years of their cohabitation, Gayoon has hidden her love for Taejun. One fateful day, she accidentally sees him indulging in self-pleasure. From that point forward, all her thoughts revolve around Taejun’s "thing"… and ultimately, she finds herself pleading with him for just a mouthful.