Aijin Hitozuma: Fushidarana Seiheki (2000)

Sawamura, a screenwriter, received a proposal from Inaba, a TV producer, as a condition for getting a project approved. The Inabas, whose marriage had grown stale, had decided to try partner-swapping; Sawamura planned to pass off his own mistress, Ryoko, as his wife so he could openly engage in an affair. When the earnest Sawamura expressed reluctance to betray his wife, Kazumi, he was told that he simply needed to avoid sleeping with his actual wife, Yukie. However, on the day itself, Sawamura found himself captivated by Yukie’s beauty and kind nature, and ultimately ended up sleeping with her. In reality, Yukie had seen through the entire scheme all along.