|Academy Grad. Age||8|
|Chūnin Prom. Age||14|
|Jōnin Prom. Age||16|
|Kekkei Genkai|| Rinnegan, |
Minor Dōjutsu (formerly)
|Nature Type|| Water Release |
18px Yang Release
|Jutsu|| Asura Path |
Flaming Arrow of Amazing Ability
Water Release: Water Dragon Bullet Technique
Water Release: Water Encampment Wall
Fire Release: Dragon Fire Technique
Fire Release: Phoenix Sage Fire Technique
Fire Release: Great Dragon Fire Technique
Sayo was born under unknown circumstances in the Land of Water, to parents who died in the Bloodline Purges of Yagura's reign over the country. Three Kiri shinobi entered the house, and killed her parents as they tried to defend her. As they attempted to kill Sayo, too, she activated a minor dōjutsu, catching them in an extremely strong genjutsu. While they were stalled, she ran past them and out the door, weeping and stumbling.
After wandering several days, Sayo was taken in by an orphanage in a nearby town. Here she was happy for a time, and made a best friend: another little girl named Koten (古典). The two of them played together, slept in the same bed, and Sayo began to open up, to laugh again, to look up from the ground she walked on. But it was not to last. The orphanage was destroyed in the crossfire between loyalist forces and a rebel group in the Land of Water, both mistakenly believing that the other would not attack an orphanage filled with innocent civilians. Hiding in the angle between the only two walls still standing, Sayo was found huddling around Koten's wounded form several days later. Again instinctively using her bloodline, she transferred most of her life energy to Koten to heal her. Yet, as she was unused to using the technique, she also transferred some of her Spiritual Energy, creating a mental link between the two. They were picked up by a masked shinobi working for Kabuto and formerly Orochimaru's base in this particular island group. Sayo, tearlines etched into her cheeks, pleaded with the leader of the base to help Koten wake up, as she was in a light coma after the trauma that had been physically healed. The lead scientist, cultivating the persona of a kindly benefactor, agreed, making him one of the people the young Sayo looked up to. Hopes high, Sayo eagerly agreed to help the Oto scientists, as they were going to wake up her Koten, right? For three months, Sayo hovered by her friend's bedside, the unnerving emptiness in the mental link a constant reminder of the condition of her only friend. After several months of this unusual mental connection being monitored and analyzed, the researchers woke Koten up, and in gratitude Sayo promised they would do anything they could to pay back the institute.
As part of this deal, the pair underwent various experiments, leading to a potent cocktail of drugs circulating through the systems of the two girls. However, Koten grew sick and could no longer stand the testing, and was harvested for DNA, organs, and tissue while still conscious. However, strapped to the next bed over, Sayo could see all. Struggling and screaming until her voice gave out, Sayo underwent extreme mental trauma, only amplified by the mental connection to her friend as Koten was butchered and died before her very eyes. This event, with the recombinant drugs circling within her system and the trauma-triggered special chakra produced within her brain, only made worse by the death on the other side of the mental link, caused drastic change. Due to her bearing a minor dōjutsu, this chakra funneled into her eyes, and they mutated and evolved into the oldest of all dōjutsu: the Rinnegan. The researchers, about to give her another injection to keep her quiet, paused for a fatal second as her eyes began to grow a rippled pattern. Manifesting the powers of the Asura Path, she ripped the scientists of the base limb from limb as she cried in the deepest human sorrow, and left a demolished base behind while carrying the body of her only friend. According to Koten's gravestone, she was eight at the time. 
She didn't get far before her newly acquired eyes drained her chakra, and collapsed outside a town in the Land of Water. Her unusually developed chakra signature did not go unnoticed by a passing Kiri patrol, and she was taken to Kirigakure while unconscious, still gripping Koten's form.
In Kirigakure, she was taken in by their shinobi program, and barely graduated, being marked down as "distracted, temperamental, rebellious, but with potential." She was placed on a team with the rookie of the year and the top kunoichi, two people she didn't despise. For this she was grateful. After enough time with her team, her depression began to abate, helped along by a cheerful sensei and supportive teammates. Once she began to train in earnest once more, her abilities skyrocketed, learning basic jutsu of all five elements.
Sayo is a very reserved person, not easily trusting or expressing emotion. She has seen too much trauma for this to happen. She suffers from PTSD, post-traumatic stress disorder, which was ignored due to her status as a valuable bloodline. The three people she absolutely trusts and uses as emotional support are her sensei and teammates. They've bonded through high ranking missions, making Chunin in their first exams, after their sensei held them back a year.
Sayo also is noted for visiting Koten's simple grave in Kirigakure, marked with her name and age only. She mentally voices her thoughts to Koten, giving her updates on how her life is going, her missions, and other data in a similar fashion to Kakashi Hatake's visiting of the Memorial Stone. 
However, she still carries the scars of her childhood trauma, and regularly takes pills to help her sleep without nightmares. Unexpected events such as a target attempting to grope her can cause both her to lose control and rip them apart in the midst of a panic attack, before passing out herself into dark, fevered dreams. 
Sayo is a powerful ninja, being an elite Jōnin and ANBU member of Kirigakure, one of the Five Great Shinobi Nations. Much of her strength derives from her affinity to all five elements due to her mutated Rinnegan. Also, she has manifested the powers of the Asura Path.
Sayo has been commented on as possessing a large and varied store of elemental ninjutsu in all five elements, making her one of the premier ninjutsu specialists of Kirigakure.
Sayo awakened her Rinnegan through genetic mutation, a combination of several events and her bearing a dojutsu.
One of Sayo's greatest hidden strengths is the Asura Path of the Rinnegan. This ability, in its most basic form, allows her to summon mechanized armor. In its intial state, she pauses fighting temporarily, as two new pairs of arms rip out of her shoulders, giving her a much more bulky torso. Also, she gains two additional faces, on the sides of her head, giving her slightly more than 270 degrees of vision. She alters the abilities manifested in her extra arms depending on the usage she requires. She has been shown manifesting high-speed drills, steel cables, and missiles instead of hands on her arms. However, she can maintain them simply as additional, semi-robotic arms for powerful taijutsu abilities. Nagato's Asura Path was strong enough to rip Jiraiya's arm off with taijutsu moves; Sayo's can match this extreme strength. This set of abilities alone places her on par with many Jōnin, disregarding her Ninjutsu prowess.