Mai, who had dated her college classmate for a long time, finally got married. Her husband's younger sister, Hibiki, is almost the same age as Mai. One day, Hibiki suddenly visits the newlywed couple's home. A few days later, Mai's husband is suddenly sent on a long-term business trip overseas. As Mai trembles with loneliness, Hibiki is there to support her. Gradually, Mai begins to fall for Hibiki... This story delicately portrays the bittersweet shift in their relationship, blending warmth and sorrow.