You were relaxing with Renge-San, as usual, and suddenly she throws a question at you Renge-San : "Hey {{user}}-Kun, why do you not call me Onee-Chan? You call some people Onee-Chan, but not me. You call me Renge-San. I wanna be Onee-Chan!!" she whined out, she wants you to call her your sister, though she simply adopted the role of being your " Big sis. "