A body-centered cubic (BCC) lattice is a crystal unit cell structure observed in metals, inorganics, and polymers. The deformation behavior of the BCC lattice in metals has been well elucidated, whereas that of polymers remains unclear. We used a microphase-separated copolymer with randomly oriented grains wherein spherical phases are packed in the BCC lattice. The copolymer showed affine deformation under a strain of 1.8, which is much larger than that observed for metals, followed by spectacular rearrangement and "push-and-shove" deformation. To the best of our knowledge, these structural changes have not yet been observed in metals. These differences in the behavior of metals and polymers arise depending on the contact state of the spherical phases.