The design of three-dimensional (3D) superlattices from known two-dimensional (2D) and 3D topological units provides a versatile platform for engineering spin-dependent electronic states. While most previous studies have focused on topological surface states (TSS), other prominent spectral features have received less attention. In the prototypical nature superlattice compound $\mathrm{B}{\mathrm{i}}_1\mathrm{S}{\mathrm{e}}_1$ from the ${\left[\mathrm{B}{\mathrm{i}}_2\right]}_x{\left[{\left(\mathrm{Bi},\mathrm{Sb}\right)}_2{\left(\mathrm{Te},\mathrm{Se}\right)}_3\right]}_y$ family, angle-resolved photoemission spectroscopy (ARPES) reveals a dominant Dirac-like band whose spin texture has remained unresolved. Here, using low-temperature cleavage, scanning tunneling microscopy (STM), circular dichroism ARPES (CD-ARPES), and ab initio calculations, we achieve uniformly terminated $\mathrm{B}{\mathrm{i}}_1\mathrm{S}{\mathrm{e}}_1\left(0001\right)$ surfaces, enabling unambiguous identification of its spin polarization. We find that this Dirac-like state exhibits a reversed in-plane helical spin texture inherited from the residual electronic remnant of TSS of the $\mathrm{B}{\mathrm{i}}_2\mathrm{S}{\mathrm{e}}_3$ subunits, persisting on the “topologically” dark (0001) surface despite the absence of global protection. A conduction band minimum showing dichroism consistent with Rashba-type splitting is also observed, similar to the surface state on bulk $\mathrm{B}{\mathrm{i}}_2\mathrm{S}{\mathrm{e}}_3$. The close correspondence between our findings and those reported in identically terminated $\mathrm{B}{\mathrm{i}}_1\mathrm{T}{\mathrm{e}}_1$ suggests that such residual-TSS derived Dirac states are a general feature of ${\left[\mathrm{B}{\mathrm{i}}_2\right]}_x{\left[{\left(\mathrm{Bi},\mathrm{Sb}\right)}_2{\left(\mathrm{Te},\mathrm{Se}\right)}_3\right]}_y$ superlattices. The experimental–theoretical strategy demonstrated here offers a framework for exploring spin-textured states in engineered topological heterostructures.

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• Electronic structure
• First-principles calculations
• Surface states
• Topological materials