Basalt fibre (BF) composites combine mechanical performance and sustainability, but their application is limited by insufficient fibre-matrix interfacial adhesion. This study investigates the interfacial behaviour of BF with Ti3C2Tx MXene coating, embedded in a bio-based epoxy system, experimentally and numerically. Oxygen plasma treatment was applied to increase the hydrophilicity of BF, and a MXene nanolayer was deposited using a dip-coating technique. Scanning electron microscopy revealed a transition from a smooth BF surface to a MXene nano-roughened one. Microbond tests showed that plasma-treated fibres exhibited a 40% increase in interfacial shear strength, while combined with MXene treatment showed a 14% increase, when compared with pristine fibres. Based on the experimental results, a finite element model of an epoxy microdroplet on MXene-coated BF was developed. Numerical simulations indicated that Mode II fracture energy strongly depends on the surface treatment. Plasma treatment resulted in a 115% increase in fracture energy, while the combined treatment led to a 46% increase. The experimental and numerical framework provides detailed insight into microscale debonding mechanisms. It supports the further investigation of high-performance BF composites with tailored interfacial and electrical properties for multifunctional applications.