Mai is Yui's older sister. The two sisters were pretty close. Mai lived with her boyfriend Sota Kitamura and worked as a hotel staff. She also briefly worked as an elementary schoolteacher just like Yui was. At some point, she lost contact with Yui, and was informed that she had disappeared. Worried about her, Mai goes in search for her, and investigates what happened to her, unaware that she fell victim of a mysterious, ruthless grudge curse. Yui's ghost begins appearing to Mai, often alongside Toshio, guiding her thoughout her investigation, and giving her hints about her fate. Mai soon understands that Yui has died and tries to understand how did it happen. Yui told Mai about Toshio and that he did this to her. A year later, Mai was sleeping with Sota in their apartment when she heard Yui's voice apologizing to her and woke up. Mai woke up again and told Sota that she's had a strange dream about Yui. In the morning, Mai came to hotel, and received a call from Yui, but did not answer it, instead saving it as a voicemail. Exiting the room, Mai listened to Yui's voicemail. In it she heard her breathing, and then a death rattle, and she found it strange. Later, that evening, Yui appeared to Mai in a hotel room and told her that Toshio is always with her and that he will not let her go. Mai, and Sota returned to their apartment and listened to Yui's voicemail together. Sota got scared by it and turned it off. Mai receives Yui's belongings, and finds Yui's former teacher book and Saeki house address. She finds and reads Kayako's journal. That evening, Sota returns home from work and sees Mai still reading Kayako's diary. She goes to the bathroom and takes a shower. Next day, she decides to visit the Saeki house and heads to the place where it once was. She is disappointed to see that there is no traces of the house left because it has been demolished and barred from being built ever again by Kyosuke Takeda, who lost his wife and sister-in-law to the curse. He comes to this place and meets Mai near an empty lot. He tells her about the house and it's fate and warns her of the curse. She tells him that Yui came to this house before her death and he reveals to her that he knows about Yui and her fate. She tells him that she must find Toshio Saeki regardless for Yui's sake and asks him for his new address. After a short hesitation he gives her Reo's adress and she sets off to her house, not knowing that Sota follows her. She arrives at Reo's house and finds it empty. Mai arrives at a hotel and sees Sota's ghost walking around it. She follows him to the elevator and finds it filled with Toshio's. Worried, she calls Sota's phone and receives no answer. She arrives at their apartment and finds Sota's dead body. Next day, she sits at the table, looks at Kayako's diary, talks to herself about the curse, and decides to get revenge, and end the curse. She heads back to Reo's house and meets with the ghosts of Reo and her mother. They present the possessed Ena as Toshio. Seeing Toshio leaving Ena's body, Mai frantically tries to escape, but is cornered by Kayako. Kayako suddenly disappears and Yui appears in her place. Yui laughs and morphs back into Kayako with horribly disfigured face. Mai sees Kayako's face and begs for help when Kayako comes closer and kills her.