This fall, Natsuki (Akari Hoshino), a teacher about to get married, and her colleague, math teacher Koichi, were enjoying the blessings of those around them alongside her sister, Shiori (Ai Mi Sakamoto). However, one person harbored deep resentment—Mai (Kosaka), a former coworker who had been fired from the school a year earlier and now viewed Natsuki and her family as enemies.