Rena has long black hair that can extend all the way down her back, but she keeps it in double ponytails at the back. At both sides of her face she has two hangs that are tied. She has a very slim frame, in comparison to Kanna's buxom one, which encomprises average sized breasts. Much like being more petite and lightweight she also appears to be the shorter of the two sisters. Her dominant outfit seems to resemble that of a nun's outfit, where she keeps her two swords, Life and Death, strapped to her left.
Defined as the "quiet" and "levelheaded" one of the two sisters, especially with her assume muteness. Rena compared to her older sister, Kanna, despite not actually being mute, chooses simply not to speak and rather she writes down her thoughts on a notepad she always carries with her. Even so, the amount of things she says are limited.
Compared to Kanna who is brash, Rena displays a high level of respect and professionalism in comparison. She treats people with respect even with her status as a demon. Her overall personality can be compared to that of which samurais and swordsmen display following the bushido code.
Rena as a member of the Royal Oni Clan is remarkable fighter born and trained to fight. In spite of such, it is noted that she isn't really the fighter type as with her dual sword, Life and Death, she has the special ability to remove demons from victims without actually cutting them. This ability has made her quite usaful to Setsuna, which currently puts her in the lead over her sister Kanna for who will become Oni Leader. Regardless, Rena in spite of being the weaker of the two Oni sisters, powerwise, has shown remarkable skill as a fighter that shouldn't be taken lightly. She has demonstrated the ability to defeat weaker demons, and was able to easily defeat a member of the Zombie Oni clan with little effort before Erionelle's interference.