Ten years ago, Kasumi divorced her husband and raised her son alone. Working tirelessly to support her child, she managed to send him to college. She struggled hard to pay his tuition, and her efforts paid off when he received a job offer from a major staffing agency. Feeling that her role as a mother was nearly complete, Kasumi began to sense a quiet loneliness deep inside. Then, her son invited her on a hot spring trip—an intimate graduation journey for just the two of them.