Koneko Toujou

Born as Shirone, Koneko is a young Nekomata who is part of a rare species among her kind, called the Nekoshou. After losing her parents, she and her older sister, Kuroka, were later taken in by an unnamed Devil who reincarnated her sister as one of the members of his peerage. However, Kuroka's power as a Nekomata supposedly soon grew out of control, eventually causing her to kill her master and become a Stray Devil on the run from her pursuers. In actuality, he had planned to harm Koneko, causing Kuroka to kill him in order to protect her younger sister.

Following the incident and the failed manhunt that came after, Koneko was sentenced to death by the Devils in hopes of preventing another incident like Kuroka's from happening. However, Sirzechs Lucifer, one of the Four Great Satans, protected her, and left her under his sister's, Rias' care. Due to the trauma she experienced with her sister's betrayal and murder of her master, she fell into a deep depression, eventually robbing her of nearly all of her emotions until Rias helped her out of it. It was around that time Rias gave Koneko her name, and made Koneko her servant.