Yumi usually never takes the train, but when she does, she finds herself in an unexpected situation. Surprised and confused by sudden groping, she remains frozen, unable to move or resist. The incident leaves a deep impression on her mind and body, and even after returning home, the memory burns vividly in her thoughts. Overwhelmed more by pleasure than fear, she gives in to arousal and begins masturbating. Yet the experience remains impossible to forget. Choosing to ride the same train again, Yumi seeks out new sensations, her actions stirring profound emotions within her.