Shounen ga Otona ni Natta Natsu

The protagonist, Ryuki Kirishima, lost his parents in a car accident when he was young and has been living with his older sister, Reiko, ever since. He thinks of Reiko as the greatest person in the world. One day, Ryuki and Reiko gathered in their secret base’s warehouse and watched a video of the rising star “Kiriru-sama” who was a hot topic on adult video websites. Ryuki was captivated by Kiriru’s large, soft breasts, her perfect waistline, and her incredibly curvy backside. He had never reacted to erotic videos before, but Kiriru was different. Suddenly, Kiriru appeared, completely naked, and they ended up creating an unforgettable summer memory together.