Keiko is a single mother who has worked tirelessly, driven by her desire to spare her son Tatsuya from hardship. Before she knew it, Tatsuya was nearing university graduation and had already secured a job. With motherhood approaching its end, Keiko began to feel a sense of relief. Yet, at the same time, she started sensing a vague emptiness within. Feeling lost, as if she had lost her life's purpose, she received an invitation from Tatsuya for a hot spring trip. Tatsuya explained, "I've lived with Mom all through university, so I'd like to go on a graduation trip," and the two set off on a journey together.