The development of sustainable electrodes through biomass valorization requires innovative strategies to overcome the limitations of conventional manufacturing processes. This study demonstrates a facile yet effective green fabrication route, without corrosive reagents or complex treatments, for high-performance supercapacitors using carbonized balsa wood monoliths (CW) as self-supported electrodes. Mechanistic investigations reveal that Cu/CuO/Cu₂O heterojunctions were formed within CW through the single-step impregnation-carbonization process. Capitalizing on the innate hierarchical porosity of balsa wood, the optimized electrode (BSC-4Cu) achieves an exceptional specific capacitance of 1164 F g⁻¹ at 100 mA g⁻¹ (9314 F cm-2). The corresponding symmetric supercapacitor delivers 154 Wh kg⁻¹ energy density at 180 W kg⁻¹, maintaining 93% capacitance retention after 10,000 cycles, surpassing commercial supercapacitors (1-10 Wh kg⁻¹) and approach lithium-ion batteries (150-200 Wh kg⁻¹). This work establishes an eco-conscious protocol for transforming fast-growing biomass into high-value energy storage devices, emphasizing simultaneous performance excellence and sustainable manufacturing principles.