Sisters (Anime)

Sisters (JAPANESE, ROMAJI), is a title given to female humans who are preparing to become Mamas. They are caretakers for orphans in the Premium Farms like Grace Field House. Sisters are previous "orphans" who have surpassed an insurmountable level of expertise in the Litany Exams and have spent a lot of time of training. They need to keep up their hard work or they may also get killed. "Orphans" are given the choice to become sisters if they lived to 12 years of age at their farm.

The other option is to be killed and have your body shipped off as human meat for demons. When a girl is picked to be a mom/sister, they are sent off to train and study about what they have to do and know to keep a plant thriving. They are also given tips on how to take care of children, clean, sew, etc. We know this based on the various stereotypical "motherly" activities shown in both Krone and Isabella's training montage.