Littles and bigs at my school are really lax.
Example: My ZTA friend said "I dont have a little brother...I want a little brother!"
Me: I got my little Joe, how about it?
ZTA: Ok sure
Me: ::waves hands:: I now make you...Joe's big sister!
Jessi's gonna spend the next week writing notes for joe and eventually gives him a mug or set of letters, then she'll reveal herself next week if Joe hasn't already guessed. Big and little sis's are a kind of friend alliance sort of thing at my school. If you want to cement a group friendship, you pimp out your littles to other fraternities and sororities. Kind of like 18th century royal families.