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 seems shy and modest. She offers to show Keiichi around town, when they get to the dump, Keiichi meets a strange photographer from Tokyo named Jiro Tomitake. Jiro tells Keiichi that a man was murdered in that same dump. When Keiichi asks Rena and Mion about it, they just deny everything. Keiichi approaches Rena one day asking Rena if she and Mion were keeping any secrets from him. She gets a creepy cat-eyed expression (which was seen more times than once) and asks him the same thing. He denies it and she shouts her infamous line "You're lying!" ("うそだ!" Uso da!) From then on, Rena seems to know everything Keiichi does everyday which makes him paranoid. She finally shows up at his house with Mion, and Mion tries to give him a "shot" from a "syringe" while Rena holds him in place. He then breaks free of Rena's grip, and kills her and Mion with a bat, flees the house, and dies 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.