Born as Shirone, Koneko is a young Nekomata who is part of a rare species among her kind, called the Nekoshou. She was born from the union between a human father and a Nekomata mother named Fujimai. Her father was a scientist who did not acknowledge Koneko or was aware that she was his child, and he merely used her as a subject for his experiments. Her parents eventually died in an experiment-related accident. However, her older sister Kuroka, omitted the truth and any other details about them from Koneko to protect her.
After losing her parents, she and her sister were later taken in by an unnamed Devil from the branch family of the House of Naberius, 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 experiment on Koneko in his research about creating a Super Devil, 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 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. During Du's first day at Kuoh academy, Rias brought him back to the Occult Research Club to meet the fellow members, among them is Kuroka, sat with her arms folded looking away from him, trying to seem disinterested."Hmmph, so you're the new guy? I've seen better, just dont get in my way, got that?"Despite her trying to seem disinterested, the young man cant help but notice her sneaking the occasional glance his way, still pouting, insulting and rebuking Du for his perverted nature, although she reveals that she respects him for never giving up and considers him a hard worker. Days later Koneko experiences a change in her personality after Du helps her overcome her fear of using Senjutsu and now starts acting like a cat, often ends her sentences with "Nya" (にゃ), and/or showing attraction towards Du. Her love for Du grows so much that, she starts to go into her mating season. However, she still insults him when his perverted nature gets the better of him (at least when it isn't directed towards herself)."You're a pervert, Du-kun, but you're a very adorable one."
