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Very long baseline interferometry (VLBI) observations show that relativistic jets, such as the one in M87, exhibit a limb-brightened, double-edged structure that has been challenging to reproduce in theoretical models. In this talk, I present a radiative-transfer framework that combines anisotropic electron distributions with “slow-light” treatment, which considers the time-evolution of plasmas during light ray propagation. Motivated by recent particle-in-cell simulations, we assume that nonthermal electron velocities are preferentially aligned with magnetic field lines. Implementing this prescription in general relativistic magneto-hydrodynamic (GRMHD) models, we produce images across multiple frequencies and spatial scales. We find that synchrotron emission is naturally concentrated along helical magnetic fields, producing limb-brightened morphologies from tens of microarcseconds to hundreds of milliarcseconds in the M87 jet. When slow-light radiative transfer is included, loop-like features of the jet are stretched and smoothed, yielding a cone-like, double-edged jet morphology consistent with observations. We further show that jet appearance and variability depend sensitively on black hole spin, offering testable predictions for horizon-scale imaging with next-generation instruments such as EHT, ngEHT, and BHEX.