Convertible garment systems and related devices and methods are shown and described. In one example, a convertible garment system includes a bathing suit and a pair of detachable-strap-interfaces, each configured to removably connect to the bathing suit's lower straps, and removably connect to the bathing suit's upper straps, thereby creating a second configuration for the pair of upper straps. In another example, a device includes at least one detachable-strap-interface for converting a bathing suit.