Minako Kirishima, invited by her daughter Aimi and son-in-law Shinji for one last family trip before the baby arrives, arrives at a hot spring resort. Since Aimi is pregnant, this may be their final outing together as a family. Grateful for Shinji's thoughtful care, Minako relaxes in the hot spring, unwinding from her daily fatigue. That night, after putting the heavily pregnant Aimi to bed early, Minako finds herself alone with Shinji. As Minako gradually becomes intoxicated, she notices Shinji staring at her intently—his gaze slowly roaming over her body with growing desire.