Pervert at the beach: Bikini thief (1999)

Overview

Yukiko, a sex worker, took her colleague Michiyo to visit the seaside guesthouse run by her widowed older sister, Isako. While in the water, Yukiko had the strings of her swimsuit untied by a lifeguard named Matsumiya; she was rescued by him but ended up having sex with him. Matsumiya used the same tactic to seduce Michiyo, managing to obtain both women's swimsuits. The next day, Isako received a video showing the two women in a compromising sexual encounter with Matsumiya. Upon learning of Matsumiya's misconduct, Yukiko confronted him—only to discover that the person who had secretly filmed them was someone else entirely.