``The Dark Matter Ratio from Spinᶜ Phase Structure. '' Paper~VIII in MEF Series

The observed ratio of dark matter to visible matter density, ₃₌/b 5. 36, is one of the outstanding unexplained quantities in cosmology. No Standard Model mechanism predicts this ratio; every dark matter candidate either introduces free parameters to accommodate it or leaves it unexplained. This paper derives a geometric mechanism for the approximate 5: 1 ratio from the broken mirror symmetry between the Quantum-wall and Anti-Quantum-wall boundaries of the T²/Z₂ orbifold sector of the K₈ manifold of the Master Equation Framework. The Spinᶜ holonomy phase _ = 5/12 accumulated across the -axis of the orbifold pillowcase — derived topologically in Paper V 15, §8 as W₁₀ₒ₄ + W₅₈₁ₑ₄ = /12 + /3 from (K₈) = 12 and the Z₃ centre of SU (3), and the same phase that generates the CKM CP-violation phase ₂₊₌ derived in Paper II 12 — acts exclusively on the U (1) Y determinant line bundle, leaving the SU (3) and SU (2) gauge fields unaffected. This shifts the effective electroweak mixing angle at the Anti-Quantum-wall from Q 28. 2^ to ₀ₐ = 103. 2^, giving: ² W^ (AQ) = ² (103. 2^) 0. 948. The resulting electromagnetic coupling of the dark sector is ₄₌^AQ/₄₌Q 4. 23 times stronger than the visible sector (Derived). Through an asymmetric baryogenesis mechanism mediated by sphaleron transitions at the orbifold fixed points, this coupling asymmetry predicts ₃₌/b 4--5, consistent with the observed 5. 36 value (Motivated). The framework further predicts dark disk formation, dark hydrogen with binding energy 18 that of visible hydrogen, and a self-interaction cross-section consistent with the self-interacting dark matter programme. The freeze-out argument is clearly labelled Motivated throughout; the Anti-Quantum-wall angle derivation is Derived.