We experimentally study the soap film flow past a rigid plate with a trailing closed filament of a small bending modulus acting as a flexible afterbody. The complex fluid-structure interactions due to the deformable afterbody shape and corresponding dynamics are studied. We find that the shape of the afterbody is determined by filament length, filament bending modulus, and flow speed. A significant drag reduction of approximately 10.0% is achieved under specific conditions. We analyze the drag mechanism by characterizing the deformable afterbody shape. Our experiment and modeling suggest that such a flow control strategy and sizable drag reduction are expected to occur over a specific flow speed regime when a suitable flexible coating is added.