Mami, a married woman living in an apartment complex in Itabashi, Tokyo, has been wed for 18 years. Struggling financially due to her husband's low salary, she takes on a part-time job, where she falls in love with Asahi, a man 19 years her junior. Overwhelmed by passion, they lose themselves in each other, forgetting work and family, as their forbidden affair intensifies. Here begins their burning, illicit romance.