Rena is the main female protagonist of the question arcs and a girl who returned from Ibaraki to Hinamizawa one year ago, she is in the same grade level as Keiichi.
She is very kind and takes care of Keiichi whenever possible, but is also naïve and is usually subject to light teasing by Keiichi, it is hinted later in the series that she loves him. She is distinguished by her obsession with things she perceives as adorable calling them kaaii (かぁいい, a slurred form of kawaii (かわいい), meaning “cute”), which are usually moekko characters or items she finds while scouring the local dump. Generally, these things are not considered cute by others.
She also utters the phrase hau (はぅ) when excited or flustered, and has a habit of repeating phrases at the ends of her sentences, most famously “kana? kana??” (かな? かな??, lit. “I wonder, I wonder?”).
Every now and then, she goes treasure hunting in the town’s trash heap, searching for ‘cute’ things to collect, and whenever she sees something that grabs her attention, she proclaims, “I wanna take it home!” (お持ち帰り, Omochikaerī) and proceeds to try and do so, becoming virtually unstoppable during these intervals.
When in “Take it Home” mode, she comically becomes stronger and faster. Despite this disarming trait, Rena is shown to be amazingly observant and perceptive about the things around her (in Watanagashi-hen, she was able to deduce that both Rika and Satoko went to the Sonozaki house by looking through the contents of their fridge and a flier).
According to Mion, while Rena might seem cute herself, people should be careful not to anger her as she becomes quite scary when angered.
When she needs a weapon, she uses a large cleaver that she found at the dump (in the anime) or a toolshed (in the manga and game).
Rena’s real name is Reina, a name she used normally before she moved from Hinamizawa to Ibaraki with her parents one year prior to the events of the story. There she discovered her mother having an affair, causing Reina to smash all the windows in her new school and assault three male students with a metal bat under the influence of the Hinamizawa syndrome. Believing herself to be cursed by Oyashiro for leaving Hinamizawa, Reina returned to the village with her father shortly after the incident and abandoned her real given name to “Rena” out of shame of her parents’ subsequent divorce, holding herself responsible and hoping to begin life anew. So as not to alarm Keiichi, Rena claims to be a relative newcomer to Hinamizawa herself. Because of the incident, Rena is sensitive about the topic of Oyashiro, believing strongly in the existence of the deity and the curse, and becoming angry and unstable whenever anyone questions it.
Rena is especially sensitive about the topic of Oyashiro; in Tsumihoroboshi-hen, her delusions about the god’s true nature go so far as to make her take the school hostage, trying to unreasonably force a police investigation into the matter.