Terahertz (THz) wave generation, confinement, and modulation via femtosecond laser-induced plasma filaments offer a promising route toward reconfigurable all-optical THz signal processing. Here, we introduce a spatial asymmetry paradigm for THz enhancement by partially blocking the pump laser to induce steep transverse gradients in the electric field. Experiments with asymmetric blocking demonstrate a significant increase in THz yield (30–60%) compared with negligible enhancement under symmetric blocking, consistent with a two-dimensional photocurrent model. Furthermore, we explore the epsilon-near-zero (ENZ) confinement effect in plasma filaments and show that dual-and multi-filament arrays function as broadband THz temporal integrators, exhibiting 1/f spectral responses and robust near-field confinement. Experimental results confirm that increasing filament number strengthens confinement and improves integration accuracy across a 5 THz bandwidth. Finally, we demonstrate near-field perturbation using a metal plate to manipulate filament-confined THz modes, inducing first-and second-order differentiation operations on the time-domain waveform, detectable in the far field. These findings establish femtosecond plasma filaments as a versatile platform for THz enhancement and all-optical calculus operations, opening pathways toward plasma-based computing circuits.