Raised by a single mother, Kanzaki Sena is a gentle-hearted, hard-working OL at an advertising agency. She lives with her fiance and co-worker, Shindou Kouki, who comes from a line of important politicians. His family, against their engagement, pushes him to marry another woman with better family connections. This strains Sena and Kouki's relationship and they begin to grow distant. Around this time, Sena meets a mysterious janitor named Moriyama Seiji and is drawn to his darkness. One fateful evening, an incident occurs that changes the destinies of all 3 characters.