We theoretically investigate near-field radiative heat transfer (NFRHT) between subwavelength Mie-resonators supporting a supercavity mode with vanishing far-field coupling—a manifestation of quasibound states in the continuum (quasi-BICs). Employing the quasinormal mode (QNM) expansion formalism, we achieve complete spectral reconstruction of NFRHT in strongly coupled resonator systems. Through precise gap engineering, we demonstrate activation of high-order hybridized gap modes that coherently amplify the supercavity resonance. Moreover, incoherent superposition between the supercavity mode and adjacent gap-perturbed scattering modes yields an integrated enhancement effect with substantially augmented radiative power. Numerical simulations show an order-of-magnitude enhancement in NFRHT power density relative to conventional Mie-Fabry-Pérot scattering modes. We validate quantitative agreement between QNM superposition and analytical expansion methods, while confirming the spectral robustness of supercavity modes against realistic geometric perturbations. This study provides fundamental insights into non-Hermitian thermal photonics and offers practical design principles for thermal radiation resonators and metasurfaces.

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• Bound states in the continuum
• Heat transfer
• Light-matter interaction
• Nanophotonics
• Near-field optics
• Finite-element method