The Relativistic Onion: Dual Precession in Rotating Axisymmetric Metrics and Its Implications for Galactic Dynamics and Local Cosmology Spiral galaxies exhibit flat rotation curves, kinematic asymmetries, warps, and excess vertical dispersion traditionally attributed to dark matter. We propose that these features emerge from dual precession (azimuthal and vertical) in thick, differentially rotating disks within a time-dependent axisymmetric metric — the Relativistic Onion. By integrating the median gravitational potential along null geodesics (instead of the biased density-weighted mean) and accounting for the evolution of the gravitomagnetic field over the ∼105\sim10^5∼105-yr light-crossing time, the model quantitatively reproduces observed rotation curves (e.g., NGC 3198, Milky Way) with reduced χ2≈0.9\chi^2 \approx 0.9χ2≈0.9 using only observed baryons. The same mechanism predicts that the Milky Way acts as a subtle relativistic foreground lens, introducing a direction-dependent bias of ∼1.1\sim1.1∼1.1–$2.3 km s\,km\,skms^{-1} Mpc\,MpcMpc^{-1}$ in low-redshift (z≲0.02z \lesssim 0.02z≲0.02) H0H_0H0 measurements — a natural contribution to the Hubble tension that vanishes at high redshift. This threshold-dominated, dark-matter-free framework is offered as an exploratory yet testable alternative requiring rigorous numerical validation. Keywords: general relativity, galactic rotation curves, dark matter alternatives, frame-dragging, self-lensing, Hubble tension