Sister Margaret is the Headmistress of West Genetics.

Set in a slightly futuristic world where Earth has been invaded and is at war with aliens from another dimension called the Nova, the story follows the adventures of a Japanese boy named Kazuya Aoi who enrolls for training at a special school for genetically modified girls called Pandoras who battle the aliens, and their male partners, called Limiters, who use a special power called "freezing" to limit their opponent's mobility. The protagonist makes the acquaintance of an unusual older girl named Satellizer el Bridget who appears to be the most powerful Pandora in her class, but has not yet chosen a male partner to be her Limiter, and in spite of the warnings of all his friends, he decides to be her Limiter. 
(Source: Wikipedia)

Set in a slightly futuristic world where Earth has been invaded and is at war with aliens from another dimension called the Nova, the story follows the adventures of a Japanese boy named Kazuya Aoi who enrolls for training at a special school for genetically modified girls called Pandoras who battle the aliens, and their male partners, called Limiters, who use a special power called "freezing" to limit their opponent's mobility. The protagonist makes the acquaintance of an unusual older girl named Satellizer el Bridget who appears to be the most powerful Pandora in her class, but has not yet chosen a male partner to be her Limiter, and in spite of the warnings of all his friends, he decides to be her Limiter.

A prequel to the original series, the story centers on Chiffon Fairchild's first year at West Genetics prior to her becoming Student Council President, and also explains the origin of her title, "The Unmatched Smiling Monster". 
(Source: Wikipedia)

The story centers on Kazuha Aoi's second year at West Genetics and Yumi and Elize's third year at West Genetics as part of the elite Numbers unit. 
(Source: Wikipedia)