Kiss-Shot Acerola-Orion Heart-Under-Blade, also known as the "King of Apparitions," was once a powerful vampire who lived in Japan. However, after a series of events, she was left weakened and on the verge of death. In order to survive, she turned a young man named Koyomi Araragi into a vampire and fed on him to regain her strength.

However, this act had unintended consequences. Koyomi became a half-vampire and was forced to live with the curse of immortality. Kiss-Shot, feeling guilty for what she had done, abandoned her name and title and took on the name Shinobu Oshino. She also took on a more childlike appearance and personality, which is why she is often referred to as simply "Shinobu" in the series.

Throughout the Monogatari series, Shinobu's backstory is explored in more detail, and we learn more about her motivations and the events that led to her becoming the character we know today.