Oz's little sister who adores him very much. After 10 years, she attends Latowidge (ラトウィッジ), a prestigious school for nobles, of which she is a prefect. She keeps in contact with Oscar via letter and causes Oz and co. to sneak into Latowidge as she wrote that she has found a person she likes.
It is revealed that she was the one who gave Raven his hat. It is hinted that she likes Raven or maybe Eliot because she tells Oz that even though he seems to hate her, he really is a gentle and dependable guy, then she said to Oz that let her be the one to return Eliot's bag and she's happy but when Oz said that he will return Eliot's bag by himself and Ada got slight of disappointed, but in the later chapters she is seen on a date with Vincent. She has a cat named Dinah and later two cats (a black and a white one). The white one was named Snowdrop.
~From Wikipedia
After Oz disappeared, she researched the Abyss in many books. These books were about voodo magic and some simmilar things. Sadly, she never found any information on the Abyss. But when she realized,she grew to harbor an immense excitement For occult and things off the mainstream like magic, ghosts, and torture… This became her hobby.