Kazuki and Tatsume live together as mother and son. Tatsume's heart is filled with warmth from their peaceful daily life. However, one day, Kazuki introduces a man she wishes to marry—Yamamoto, a young man three years younger than Tatsume. Suppressing his concern for his mother, Kazuki begins an intense relationship with Yamamoto. That night, Tatsume accidentally discovers that Yamamoto is a marriage scammer. Learning the truth, Tatsume resolves to confront Yamamoto to protect Kazuki.