Confinement produces mesonic bound states, but their existence alone does not determine the statistical organization of the many-body spectrum. We investigate this connection in the spin-$\frac{1}{2}$ XXZ chain subject to a longitudinal staggered field, using symmetry-resolved exact diagonalization for spin chains of up to $N=22$ sites. As the exchange anisotropy is increased into the antiferromagnetic Ising regime, the finite-size spectra cross over from Gaussian-orthogonal-ensemble-like statistics to reduced level repulsion. This evolution occurs in both the zero-momentum and generic nonzero-momentum sectors examined. Direct measurements of the domain-wall-number operator and its eigenstate variance reveal increasingly sharp approximate domain-wall sectors, accompanied by banding of spin correlations and bipartite entanglement. Statistics within a selected domain-wall band further characterize the spectral organization beyond the full-sector gap-ratio analysis. We identify the one-meson branch and compare its energies and level spacings with established Airy and semiclassical descriptions and a finite-chain strong-anisotropy treatment, quantifying their accuracy and systematic deviations. These results connect the known confined two-spinon spectrum to the broader finite-anisotropy organization of many-body eigenstates and provide quantitative evidence for emergent domain-wall constraints in the full microscopic Hamiltonian.

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• Eigenstate thermalization
• Magnetism
• Quantum chaos
• Spinon
• Spin chains