As a young child, Guren came from a small village where presumeably she was shunned by others not unlike Naruto because of her unique powers. Later, Orochimaru appeared and destroy the entire village single-handedly. He was intrigued by Guren's powers and offered for her to come with him. In truth, Guren chose to follow him because she envied his power. Quickly, she became one of Orochimaru's most powerful and loyal subordinates. Eventually, she was offered to become one of Orochimaru's future vessels. When Sasuke Uchiha defected from Konoha, as Kimimaro was no longer a suitable vessel for Orochimaru, Guren became the next best choice in Orochimaru's eyes. Unfortunately by the time she arrived, Orochimaru couldn't wait any longer and instead chose Gen'yumaru. Feeling no longer of use to Orochimaru, Guren went into isolation until she was needed again by Orochimaru.
Guren has shown to be a very mysterious kunoichi, apparently preferring to keep to herself despite having a strong loyalty to Orochimaru. Her loyalty is not unlike that of Kimimaro as she too was at one point a willing canditate to become Orochimaru's next body. During her introduction, she quickly showed herself to be a remorseless and sadistic person. When told by Kabuto that several prisoners would be fighting to the death, she became ecstatic to hear there would be a slaughter.
She is devotedly loyal to Orochimaru, so much that she fell into despair when she learned she would not become Orochimaru's next vessel. It has also been shown she has a terrible relationship with Kabuto
Jutsu
* Crystal Release: Aqua Fissure Bombardment
* Crystal Release: Crystal Needles
* Crystal Release: Crystal Pentagonal Prison
* Crystal Release: Snowflake Shuriken