menstrual sister 

one of two (or more) women who happen to fall on the same menstrual cycle. Menstrual sisters often times find comfort in sulking, eating, complaining, and causing a scene together.

My menstrual sister, from the stall next to mine, threw a tampon at me as I kicked my door in anger.

As a good menstrual sister, I shared my chocolate as we bled and weeped together.

menstrual sister by PrincessGaylordFocker December 11, 2016