GOUL-006 Swept away by sweet temptation, I, the virgin Suzuki Mayu, indulged in middle-out sex with her older sister

College student Taichi, 20 years old. Yuua is his first girlfriend and he really wants to lose his virginity with her. Then one day, he is invited to her house. This is my chance to graduate from being a virgin! he thinks. But then he finds out that she lives with her older sister who will be introduced to him. This might be impossible... he gives up and goes to her house but meets Mayu-san, who is more beautiful, cuter, and has bigger breasts than his girlfriend. 'Taichi-kun, you're a virgin right? The first time is important so let me be your practice partner...' she whispers in his ear.