Yin and Yang

Ying and Yang were two loyal arrancar girls who serve Sōjirō Kusaka in the movie Bleach: The DiamondDust Rebellion. They appear to be twins, of them Yang has red hair while Ying has blue hair. They are capable of using fire and electricity with the power of their respective zanpakutōs, of which Yang's takes the form of a flaming sword with a red tassle on the bottom of the handle, Ying's takes the form of a whip with a blue tassle on the bottom of the handle.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. 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.They were sent to steal the King's Seal by Sōjirō in order to destroy the Seireitei. When Ying and Yang returned to Kusaka (Escaping Ichigo Kurosaki and Rukia Kuchiki by summoning hollows, which were later destroyed by Uryū Ishida), they were transformed by Sōjirō Kusaka when they were encased in ice to become something like Guardians,(to protect Sōjirō Kusaka) which they can attack with fire and electricity respectively. It seems that the guardians have high speed regeneration as shown in the movie when Soifon attacked Yang with Suzumibachi twice, which is suppose to destroy it, regenerated and attacked Soifon, only to be stopped by Yoruichi Shihōin. It is unconfirmed whether they were naturally-evolved like the Privaron Espada or if they were artificially-evolved through use of the Hōgyoku by Aizen.