Popular sisters Nene and Nana are invited by married elder sister Nene and her husband Shinji to join them and Nana's fiancé, Koki, on a hot spring trip. However, the inn they arrive at is bankrupt, the owner has fled, and yakuza have taken over. Unaware of the danger, the two couples are threatened and deceived, ultimately getting caught up in an extreme experience of partner swapping and creampie-filled threesomes.