Tsubaki is Black ☆ Star's Weapon and it was her the one to chose to become this.
She's the kind of girl that hides her feelings or thoughts in order to don't insult her friends, or just other people. She's friendly and kind with anyone and usually she is a peacemaker (especially with Maka and Soul's arguments). Anyway, she can have temper too, and she shows it many times, especially during the missions she makes with her Meister.
She had a really unlucky life with her family. She was chosen as heir of the Nakatsukasa family, even if she had a brother, Masamune. Actually, her skills were alyays very good in any kind of training. In one mission, she had to fight against her own brother, in order to defeat the kishin that was growing inside of him. Obviously, it was a very sad decision, but she wanted to do it with her hands, because that was her brother.
Although she's friend of everyone, I can really say that Maka is like her bestfriend, because they talk very much each other, of every kind of problem. They give themselves precious advices, especially when it comes to talk about Soul or Black ☆ Star.
We can see that many of her abilities are gained during the trainings or the missions she makes in the manga. They are: Kusarigama, Dummy Star, Ninjatou, Kage ☆ Boshi (Zero no Kata Masamune; Ichi no Kata Rengoku; Ni no Kata Tsukiyoha; San no Kata Zetsuei; Yon no Kata Edayami), Shuriken, Tamashii Kanchi Nouryoku, Youto.
Her Japanese seiyuu is Nazuka Kaori.