This paper establishes a universal equivalence principle emerging from a novel kinematic pathway to relativistic dynamics. Beginning with angular momentum conservation, we derive the relativistic energy-momentum relation, revealing rest mass as an integration constant. This approach unexpectedly bifurcates into two distinct mass-energy descriptions whose mathematical incompatibility resolves into profound physical insights. We demonstrate that: (1) Dark matter manifests as the difference between kinematic and gravitational mass-energy, M_dark = m_K - m_G, with galactic calculations showing striking agreement with observations; (2) Dark energy emerges naturally as the cosmological-scale expression of this mass duality; (3) The Hubble tension finds potential resolution through scale-dependent kinematic effects. This framework unifies phenomena from nuclear binding energy to cosmic acceleration through a single kinematic principle, suggesting that dark matter and dark energy are not substances but relationships emerging from relativistic dynamics.

This work builds upon the author's previous research in relativistic kinematics and foundational physics.