Yuna visits her in-laws' home to check on her injured father-in-law, Toru, who was hurt in an accident. Five years after losing his wife, Toru has been depressed, and Yuna hopes to cheer him up. One day, while helping him bathe, he suddenly pins her down. His deep, invasive kisses—tongue probing, lips devouring—shake her emotionally, and the lewd sounds of intense cunnilingus fill the room as Yuna, trembling yet aroused, experiences her first orgasm. Taking advantage whenever her husband is away, Toru continues to pleasure her with his obscene tongue, gradually ensnaring both her body and soul in their forbidden affair.