Byakuya Rinne is described as a very pale girl that is very kind, she has a slender body and long black hair described as amazing. She has a very relaxed face at all times.
She is almost all the time wearing her school uniform which consists of an traditional sailor uniform with black knee-high socks. However, when she takes command of a strange cult, she is seen wearing a richly decorated black bure.
In the true end, she resembles a machine rather than a human. She appears thinner than before, both her arms replaced by mechanic ones and possesses strange hair looking with hands at the ends that she is able to manipulate.
Rinne appears as a quiet girl, and looks composed in all situations, no matter how alarming. Keisuke is never able to read her detached expressions, which makes him furious and makes him want to defile her more.
As the game proceed, it is revealed that her true timeline story would be like this: Rinne was born by the female leader of a mysterious cult (which locate near the facility) > Getting rejected by her mother, who is also the leader of the cult, because of her undetermined sex due to hormone disorder > The cult attacked the hospital and kidnapped a boy (later it was revealed that boy was Keisuke) > Her mother raped him and got pregnant > The scientists of the facility got to know about the cult so they came and took Rinne and her mother's fetus back to the facility to performed some experimented on genes > Thanks to the experiments, Rinne became a girl and came back with her mother > Still got rejected because her mother insisted that The Messiah (nickname of the leader of the cult) must be a boy > Her mother and the cult planned to attack the facility > Scientists released virus to kill everyone in the cult > Rinne survived thanks to the antibody she achieved during the previous experiments > Rinne decided to come back to the facility to continue to be the test subject for the project "Paradise" > Get connected forever to the machine > Met her "father" (Keisuke) there and helped him to escape from that facility.
During the true ending, Rinne becomes gradually less human because she was used as an emergency generator to replace the original sleeping beauty, Nemu. The constant connection of her to "paradise" greatly frustrated her. However, it is stated that she accepted her awful fate.
She was the leader of a strange cult that schemes against Nemu's order. In her own path, she completed to overthrow Nemu and her follower and then to violently torture Nemu in order to reach "paradise". Rinne was birthed with an undetermined sex, and various experiments were conducted on her. When she was born and they found out she was a girl, her mother abandoned her because the messiah had to be a male. Rinne was a girl, so she wouldn't be able to fulfill the prophecy.
In episode 6 of the anime, she marries Keisuke and has a daughter.