Fate character. BB as she appears in Fate/Extra CCC and Fate/Grand Order.
Appearance-wise, she looks like Matou Sakura, with long purple hair and purple eyes. Her normal outfit is a Dracula-like black coat with a high collar, a white shirt with a large red neck ribbon, a black high-waist skirt (that emphasizes her large breasts), and thigh boots.
Not to be confused with BB (Swimsuit Mooncancer) (Third Ascension). Both wear a similar black cape, but BB (Fate/Extra) wears it with a high-waist skirt, while BB (Swimsuit Mooncancer) wears a white leotard.
This tag implicates bb_(fate) (learn more).