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 Zanpakutō 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.

Synopsis
During the ceremony to move the King's Seal, Ying and Yang appeared and attacks the royal carriage. They battled Hitsugaya shortly before he turned his attentions to Kusaka. Later, they follow Hitsugaya to the real world and battle Ichigo, but are forced to retreat.

Once the Shinigami deem Hitsugaya a traitor, they attack Ichigo once more. They prove to be a formidable match for him, but are surprised by the interference of his friends. Chad's El Diablo deflects Yang's fire blast and they send hoards of hollows to attack, but are no match for Ishida's volley of arrows. Ichigo and Rukia leave for the Soul Society to find Kusaka.

After Kusaka breaks the King's Seal, he orders for Ying and Yang's return. After noticing they lost, Kusaka encases both of them in a block of ice, seemingly killing them. However, this is not the case, as they are seen as giant Hollows once the King's Seal seals a large area within a barrier. They attempt to stop the shinigami present within the sealed area. Yoruichi Shihōin and Soifon decide to hold them off, and Soifon manages to defeat one of them with her zanpakuto's special ability, but she immediately regenerates and survives, due to the effects of the King's Seal. They are both finally killed when Ichigo and Hitsugaya defeat Kusaka, which dispels the dimension created by the King's Seal.

Zanpakutō
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.

Hollow Forms
After Sōjirō Kusaka acquires the King's Seal, he transforms Ying and Yang into Hollows. They have displayed a few abilities in these forms that they did not display in their humanoid forms.

High-Speed Regeneration: When Kusaka transforms them into Hollows, they appear to have High-Speed Regeneration after one of them was defeated by Suzumebachi's special ability, but this is due to the effects of the King's Seal, for Mayuri Kurotsuchi states that "life and death becomes trivial", and Suzumebachi's special ability is fatal.