Yin and Yang

Ying and Yang were two loyal arrancar girls who serve Sōjirō Kusaka in the movie Bleach: The DiamondDust Rebellion.

Appearance
They appear to be twins, of them Yang has short red hair and Ying has longer blue hair, parted in pigtails. The remnants of their hollow masks act as a headband that goes vertically down the middle of their head before reaching their eyebrows. They are seen carrying their zanpakutos which are a flaming sword and whip, respectively. They wear the same outfit, a white sleeveless jacket and gloves up to their elbows with bracelets on each wrist.

Zanpakuto
Yang wields a sword that is constantly covered in flames. Ying has a long whip that generates electricity.
 * As seen in the movie, both of them can combine their attacks such as when they fought with Ichigo Kurosaki, who blocked it with Getsuga Tenshō.

Transformation: Apparently, they themselves can transform into the "elements" like Yang turning into a flaming ball while Ying becoming a blue disk-like shape when they attacked during the transportation of the King's Seal.
 * High Speed Regeneration: They were seen to regenerate after Soifon hit them with Suzembachi twice, which is supposed to instantly kill you.