She was born in Hinamizawa. She then moved to Ibaraki. She was haunted numerous times by Hinamizawa's god Oyashiro-sama. Rena finally had enough and smashed all the windows in her school. After, she had counsiling to find out what was wrong with her. She kept on mentioning the name Oyashiro. Finally, one year prior to the show, she moved back to Hinamizawa and changed her name from Reina to Rena.
At first, Rena seemed shy and modest. She offered to show Keiichi around town, when they got to the dump, Keiichi met a strange photographer from Tokyo named Jiro Tomitake. Jiro told Keiichi that a man was murdered in that same dump. When Keiichi asked Rena and Mion about it, they just denied everything. Keiichi approached Rena one day asking Rena if she and Mion were keeping any secrets from him. She got a creepy cat-eyed expression (which was seen more times than once) and asked him the same thing. He denied it and she shouted her infamous line "You're lying!" ("うそだ!" Uso da!) From then on, Rena seemed to know everything Keiichi did everyday which made him paranoid. She finally showed up at his house with Mion and tried to give him a drug. He then broke free of Rena's grip, killed her and Mion with a bat, fled the house, and died in a phone booth outside of town.
Rena's dad starts dating a woman named Ritsuko (better known as Rina) and Rena finds out that she knows Teppei (Satoko's uncle) and that they're trying to get Rena's dad's money. Rena then forms a deep hatred for them. Later, Rina visits Rena at the dump and asks if she likes her. Rena asks why she's asking and tells her she won't let her marry her father. Rina tells Rena she's pregnant and attemps to choke her. Rena gropes around near herself and comes upon a peices of glass, which she uses to cut Rina's abdomine and break free of her grasp. She quickly regains her breath and grabs a nearby pipe and beats Rina to death. She then heads home and finds Teppei beating up her dad, demanding money. As he leaves, she calls him over and offers to take him to see Rina. He agrees and follows her to the dump. When they near Rina's dead body, she switches off her flashlight and says the battery died, and that she is going to find a new one. He reaches into his pocket and pulls out a lighter and lights it. When he doesn't see her, he calls for her. Suddenly, she appears behind him, holding her cleaver up in the air, then she angrily swings down, onto his head, and kills him as well.
Later, she tells Keiichi that 'Hinamizawa Syndrome' was caused by a species of parasite that lives in a swamp near Hinamizawa. He didn't believe her. She then ran away from the village only to come back and hold the whole class hostage. She says she'll blow up the school with a homemade bomb. Keiichi defuses the bomb and has a duel with Rena. During the duel, Rena begins to regain sanity and wins the duel. She forces herself to spare Keiichi and begins to cry in his arms. She then apologizes and all is forgiven. In the end of the episode, Rika is called into Ooishi's car and the whole story starts over.