A widow in mourning clothes, I want...

Izumi had just lost her husband Nishimura. Nishimura had fallen down the stairs while drunk. One day, she found a tape with a woman's voice among his belongings. Izumi suspected it was evidence of an affair. A few days later, Izumi met Nishimura's friend Fujii and played the tape for him, asking if he knew who Nishimura was having an affair with. Fujii said he had no idea who the voice was, so it wasn't necessarily an affair. However, Izumi suspected that Nishimura had whistled the same tune as the woman on the tape, and that he thought she was a boring woman compared to that woman. Fujii took the tape and said he would dispose of it. One day, when Izumi returned home from shopping, Ayaka, who she had passed in the hallway of the apartment building, was whistling the tune. That night, Izumi had a nightmare in which Nishimura and Ayaka were making love. The next day, Izumi approaches Fujii, wanting to get revenge on Nishimura for betraying her.