In human form, she takes on the appearance of a young, tall woman with large breasts and an alluring figure. She has short violet hair with long strands on each side of her face that curl up and around to resemble her tail. The bauble she wears in her cat form can be seen below her neck. She has a set of purple cat-like ears with pink tips instead of human ears, which are initially hidden by her hat. Her black witch's hat coils around at the end and retains her bright yellow cat eyes. She also has a curled up purple cat tail that resembles her cat form one. Her lips are curled like the shape of a "3" to represent those of a cat. She also has two little sharp fangs in her mouth in human form like a cat's. She dresses in many types of revealing clothing such as tank tops and bikinis, but her signature witch outfit consists of a black-blue dress that shows off her shoulders and wraps around her neck, long, open sleeves that reveal her hands and shoulders, a short skirt with a white frill and long high-heeled boots that curl upwards at the toes.
In cat form, she is a purple cat with large yellow eyes, ears with pale bushy tips and a long curly tail. She wears a smaller version of her witch's hat and a collar with a round bauble that has three triangles etched into it to resemble a jack-o-lantern's face.
Blair is very good at understanding other people and even showing kindness to others who are troubled. She is always looking for some fun, whether it is harmless or not. Playful and fun-loving, she is quite an affable person. She is well endowed, which is used when she flirts with Soul, usually by appearing out of her cat form in little to no clothing. Blair has no shame in exposing her naked body in the presence of males, exemplified by when she pulls down her towel in front of Soul and Maka's guests. This is most likely due to the fact that, in her cat form, she is always naked.
Blair was apart of a Witch clan within the Underworld, in the country of Tartarus in particular, and seemingly a well-liked member of the clan. One day, as she was taking a bath (according to her), she was confronted by a pack of Houndours lead by Hellgar, and asked to join Sombra. Believing she would lose her freedom altogether, she refused to join up. This resulted in Hellgar destroying her home, and making her flee the Underworld completely.
Blair appeared over inside Karma Akabane's house, making a meal for herself and sleeping with him before asking if she could stay the next morning as a method to make him more comfortable with her around. After some prompting, Blair was allowed to stay with Karma, and she explained her situation to the others. Once she found out Nagisa Shiota's connection with the Overworld, she immediately asked if they could go to the Underworld to get revenge on Hellgar, to which they refused. She decided that she wasn't going to leave them until they do.
Her role throughout Season 2 is mainly a supportive role.
After leaving London, and going into Amestris, she took the time to explore around a seaside town. As she was hunting down some mice as her cat form, she ended up coming across Alphonse Elric, who after some prompting decided to take her in. She stuck around with him, but as Sebastian Michaelis arrived and things started to escalate, she revealed her true self to them all. She tried to flirt with them, but she only ended up getting hit by Edward Elric, before they all went on their way to catch up with the others.
After the Pluton attack, Blair joined Alphonse in looking for any survivors when they came across Envy. Feeling sorry for him in such a state, she decided to take him back, using Alphonse as a carrier for him as they left Central, and off to the countryside. She tried helping out Envy when he did wake up, and when he did run away from them, it was her that found him alone. She explained to him her reasons for not joining with Sombra, and that Envy truly wasn't as bad as he brought himself on to be, even if he did kill her. She offered to let him join their group, and kept him dry on the way back.
Her role throughout Season 4 is mainly a supportive role.
When the groups split to find their demon targets, Blair went with Karma Akabane to face the Slicer Brothers. While finding him was no problem, she ended up brutally stabbed by Olivier Armstrong, as she was used as a hostage by the Slicer Brothers. She didn't lose any of her lives in the encounter however.
After the others were captured, she joined Nagisa and Aladdin to return to the Underworld. On this trip to find Abaddon, Blair ran into her old clan members, whom of which she was more than happy to see again. While they did have to stay overnight, Blair was offered to stay home again, but decided to stay with Team Harmony for the main goal.