Shinobu Oshino - Yenra Picture Wiki
Shinobu Oshino of Monogatari is a girl who lives with Meme in the abandoned building.
She appears to be an eight-year-old girl, but she was originally a beautiful vampire named Kiss-shot Acerola-orion Heart-under-blade who has lived for more than 500 years (and happens to be the vampire that bit Koyomi.) After the events at the end of Koyomi Vamp, she was left in a weakened condition with no powers or traces of her original personality, and therefore had to abandon her former name. She was named Shinobu by Meme at the beginning of Hitagi Crab, suggesting her kanji name Shinobu, having "heart" under "blade", matches with her original personality (but in typical Nisio Isin playing with kanji, the pronunciation of the kanji means "fern")