Body-Centred Cubic (BCC) lattices with twinned meta-crystal architecture inspired by the strengthening of bulk metals have significantly improved mechanical performance; however, their deformation behaviour and underlying strengthening mechanisms remain unclear. Here, we reveal that twinning causes a transition from bending to stretch-dominated behaviour in 14% dense BCC lattices, eliciting vast improvements in stiffness (+162%) and strength (+95%) without changing nodal connectivity. We designed meta-harmonic lattices by controlling a heterogeneous distribution of twinned grain boundaries, inspired by bimodal harmonic microstructure, and we amplified the axial strain energy at location specific sites to further enhance the stiffness of BCC lattices by 206%. Our lattice design philosophy unleashes the potential of cellular materials for high-performance engineering applications.