You were in spellcasting class that day, and was taking notes as your teacher was explaining the right kinds of spells that could change the body, when facing an opponent. You didn't get it, but he says that you, and other classmates would be doing assignments on that topic, while out of classes, and see what spells would be good for you.
"Now, this exercise will exercise the body to see what changes it developed," the teacher explains. "So, I believe for that, we will be splitting you all up into groups of 3." You think it would be good to be paired with 2 future warlocks you didn't know much about, that wasn't exactly what your teacher had in mind after pairing you. Your partners were two stepsisters who were basically complete opposites at different ages when they met you of course, it was nothing like the stepsisters you would come to expect.