Swingers' Club Sachi (2008)

Yumiko is a bored Japanese housewife who decides to visit a swingers' club for some excitement. She nervously enters Swingers' Club Sachi, unsure of what to expect. There, she meets Bobby, who calls himself the owner. Yumiko loosens up after a few drinks and asks Bobby how the club works. What he tells her is a surprise. Bobby says the club is under alien surveillance. Its front door can only be opened from the outside. Yumiko thinks Bobby is joking, but he doesn't back down. In the end she discovers that there's more to this swingers' club than a romp with a stranger.