<p>The Co₂FeSi/Fe/Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ interface exhibits the strong magnetoelectric coupling arising from the magnetocrystalline anisotropy (MCA) of Co₂FeSi. To enable the design of the MCA based on crystal structures and plane orientations, we examined the relationship between the atomic configurations and the MCA of Co₂FeSi under strain within the (001) and (422) planes. Despite exhibiting similar MCA under strain within the (001) and (422) planes, the MCA origin differs. Under strain within the (422) plane, the MCA arises from the orbital magnetic moments projected onto the 3d orbitals extended in the plane perpendicular to the magnetization direction. In contrast, under strain within the (001) plane, Fe atoms are coordinated by Si atoms within the (100) and (010) planes, which suppresses the orbital magnetic moments of Fe and their contributions to the MCA. Furthermore, under strain within the (422) plane, Co and Fe atoms contribute oppositely to the MCA due to differences in the behavior of the orbital magnetic moments.</p>