|Witches in the East|
Azuma no majo
Chapter 16 (mentioned)
Episode 19 (mentioned)
The "Witches of the East" possibly alludes to the Witch of the East from The Wizard of Oz, as well as that book's many adaptations in popular culture.
Not much is known about the strength of the Witches of the East, though Death mentioned witches around the time period of eight hundred years ago prior to the founding of the DWMA caused far more damage then they do in the present time.