A remote controller for controlling a remote unit includes a stationary button assigned to a first function of the remote unit, and a first flexible button assigned to a second function of the remote unit and configured to be addable to or removable from the remote controller. The remote controller may further include a base, a membrane layer mountable on the base, the membrane layer including the stationary button and a first flexible button base, a first flexible button cap mountable on the first flexible button base to form the first flexible button, and a first face mountable on the membrane layer and having a first opening pattern exposing the stationary button and the first flexible button.