PERSONALITY
She is very kind and takes care of her friends, but is also naïve and usually subject to light teasing. She is distinguished by her obsession with things she perceives as adorable, calling them kāii (かぁいい), which are usually moekko characters or items she finds while scouring the local dump. Whenever she sees something that grabs her attention, she proclaims "I'm gonna take it home!" (お持ち帰り〜) and proceeds to try and do so, becoming virtually unstoppable during these intervals. She also utters the phrase haū (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?).*
Rena may appear cute at first glance, but her scary side sure is shown. She can be cruel and quite creepy, as she hold hostage an entire class without much problem. Lies are something she surely hates— yelling her iconic phrase when she recognizes a lie: 嘘だ!. When someone mentions Oyashiro-sama in a lighty tone, Rena won't allow that. She will then act hostile, as she believes in the dentity and Oyashiro's punishment against her for leaving the village.
When her creepy mode is on, she will be the first one to attack and yell. Or in simple talks like the first 'fight' with Keiichi, her voice lowers in such a scary tone, with blunt and harsh answers.
*: wikipedia