Physically, Renge is identical to Kurenai, save for the small marks under her eyes. Renge is fairly tall and slim, as well as having a prominent bust. Her hair is light brown, like that of Kurenai's, however it tends to stick up a bit, like Kurei's does at times. Renge's clothing is also an exact copy of Kurei's, something he mocked her for.
Renge's mind is like that of a naive little girl, despite appearing to be a woman in her late teens. She follows Mori Koran's orders without question because she believes he is her father. Renge has little knowledge of right and wrong, and does as she's told to please her father. This is likely due to mental implants on Koran's orders to prevent her from growing out of control, like Kurei did.
Renge is friendly to most she meets, but this does not mean she cares for their well being. Her mental state seems to deteriorate as time goes on and by the time she encounters Kurei, she seems to have become insane.
Part in the Story
Ura Butou Satsujin Arc
Renge is not seen until the end of the tournament when Mori Koran ambushed Kurei, who was in a state of weakness and exhaustion after his battle with Recca. Renge impaled Kurei with her arrows of flame, and he was rescued by Neon.
In the anime, she was seen in silhouette inside the water tank Koran secretly kept in his office after Kurei left to battle Recca's team in the finals of the tournament.
Sealed Lands arc
Later on she helps Koran against Recca and his allies and after his merge with Tendou Jigoku, she escapes with him along with Aoi and the others.
After Aoi successfully retrieved Yanagi Sakoshita and imprisoned her within SODOM, Renge is seen with Mori, who tells her that she was special to him and that she had to "think of nothing" and "become [his] strength." She later encounters Aoi, and she cheerfully greets him, only to be coldly put down. Unable to fathom why he treated her so, she continues talking, insensitively talking about her experience with Mori. Disgusted by how well she was treated by Mori, Aoi pins her against the wall and tells her that he couldn't care less about her "bragging," then leaves to see Yanagi. Renge herself returns to her child-like room, and tears apart a teddy bear after it (logically) fails to answer her question about Aoi's treatment of her.
Afterwards when Kurei comes to annihilate Koran (now one and the same with Tendou), she tries to stop him, but this time, he easily breaks through her and when he's about to kill her, she runs off, experiencing fear for the first time in her life (since she'd never been handled so easily). She tells Koran, whom she calls "father", to help her, because Kurei, whom she calls "brother", is trying to kill her. Tendou Jigoku instead devours her in order to gain her power of flame, so that he can have a much stronger defense against Recca's flame attacks (since he and Recca are encountering each other, at the time).
Renge is the successful result of a cloning project to duplicate Kurei's powers in the body of an obedient killing machine. Renge's primary power is firing arrows of flame, which she used to impale Kurei while he was in a weakened state. She was even able to fend off Hokage for a brief period of time. She could also fashion a blade of fire around her hand.
However, despite being fairly powerful, Renge's inexperienced mind is her greatest weakness. She has no knowledge of battle tactics and as stated by Kurei, she was far weaker than Recca. Also, possibly due to lack of understanding of Kurei's true power, her flame possesses no true form.