BPT diagram for the narrow emission lines in LRDs. DESI DR1 LRDs are shown in blue. The z  <  0.3 LRDs from Paper I are shown as orange squares, and the z = 2.26 LRD from I. Juodžbalis et al. (2024) is shown with a green diamond. The emission-line galaxies at z = 1.4–7.5 from A. E. Shapley et al. (2025) are shown with gray circles. The classification boundaries for different ionization mechanisms (G. Kauffmann et al. 2003; L. J. Kewley et al. 2006) are shown as blue solid and dashed lines. The corresponding regions are labeled.