Yamagishi, Yoshino, Iida, and Niiyama are a group of four close friends. Yamagishi has secretly had feelings for Iida for a long time but has never confessed. Yoshino is always cheerful, particularly interested in sexual matters. One day, while Yoshino was bragging to Yamagishi about a new dildo she bought, Niiyama and Iida overheard. Out of curiosity, Iida demanded to go to Yoshino's house to see it. Curious about how to use the dildo, Niiyama asked Yoshino to use it in front of her for observation. However, despite trying, his penis remained flaccid. Yoshino then suggested Niiyama show her panties to help him masturbate, but unexpectedly, Niiyama complied immediately! And then, the two gradually progressed to sexual activity, right in front of Iida and Yamagishi. The two just silently watched their close friends have sex in front of them. But after Niiyama finished, Yoshino called Iida. Yamagishi thought Iida would refuse, as she would never do such a thing just out of curiosity. He believed that until Yoshino pushed his penis deep into Iida's vagina...