Hikaru, the older sister, was plotting to take her younger brother Masaru's virginity. Even Masaru, who was in his teenage years, was conscious of Hikaru. When Hikaru persistently seduced Masaru without a bra, Masaru, unable to resist, tried to touch Hikaru's budding breasts while she was sleeping. However, it was a trap set by Hikaru! The next day, Hikaru blamed Masaru for this, and instead of forgiving him, she made him wear an eye mask and put her hands on the zipper of his pants...