On my campus, it was always a big thing that if you were good enough friends with a sorority member, she would ask you to be the "big brother" of her sorority little sister. Basically you would just introduce her to fraternity life at the school, introduce her to the guys and help out with her getting used to Greek life. I had an Alpha Phi little sis, and we ended up becoming good friends.
As far as having a "Big brother/little sister" relationship with another organization, though, I know Kappa Sig does not allow that sort of relationship.
|