While active safety has become a focus of attention, passive safety protocols are still being updated, and evaluation standards are becoming stringent worldwide. This paper focused on FMVSS 301, the North American regulation for rear impacts. Due to an offset impact with deformable barrier, it is challenging to control bending modes of rear frames. Furthermore, there is a considerable difference in load paths to the left and right frames, and the amount of bending deformation experienced by the frame on the non-collision-side, which does not directly contact with the barrier, is low. The purpose of this research was to enhance rear-frame energy absorption efficiency in such collisions. To achieve this goal, this research focused on enhancement of deformation mode of the rear frames, and also minimizing the difference in their input loads. For the enhancement of deformation mode, the number and arrangement of collapse points were optimized, and multi-stage bending mode with a high level of energy absorption efficiency was achieved. A partial softening was applied to create an initialization point of bending deformation. In order to reduce the difference in load paths, the length of the central flat section of the bumper beam was set such that the area of impact with the barrier would be symmetrical on both left and right sides. To maintain clearance between the barrier and the bumper beam-end on the collision side for as long as possible, geometrical beam parameters such as bending angles of the beam were also optimized. A stretch bending method was applied for the manufacturing of a prototype beam. This increased the amount of energy absorbed by the frame on the non-collision-side. Impact tests conducted using drop tower tests, which satisfy geometric specifications for mass-production, verified that this approach increased rear-frame energy absorption efficiency by 220%.