Mariko is Rika's friend and elementary teacher. One day, Rika went to the Saeki house, and met with the resident ghosts. After an encounter with Kayako, Rika was left in shock and taken to the hospital. Mariko visited her and went to get some drink. She walked out of Rika's room and met detective Nakagawa outside. He entered Rika's room and Mariko walked away. When she returned, she overheard Rika talking with Nakagawa about the house. Nakagawa walked out of the room and met with Mariko again. She bowed to him and entered Rika's room again, while Nakagawa went to phone his partner. She left the hospital later, and Rika was discharged from it soon after. At some point, Toshio became Mariko's student and then suddenly stopped coming to school. She was concerned about him and tried to reach his parents, but to no avail. Then she called Rika and invited her for dinner. Rika met with Mariko and they went to cafe. Mariko tried calling Toshio's parents again, but didn't get reply again. Mariko told Rika that one of her new students isn't coming to school and that she can't reach his parents. She mentions that she's going to check in on him as he has not been in school for weeks. Rika looks under the table, sees Toshio, screams in fear, and falls from the chair. Mariko runs over to her, tries to calm her down and helps her to get up on her feet. Later, Mariko goes to the Saeki house and meets with Toshio. She phones Rika and tells her that she's at her pupil's house, checking in on him. Rika hears meowing in the phone and asks Mariko, where is it, when she hears meowing even louder and the call cuts off. She realises that Mariko is at the Saeki house and rushes to save her before it is too late. Mariko, however, is killed by Kayako before Rika can save her.