This study introduces a decellularization-inspired strategy to isolate the tissue scaffold from the green macro-algae Ulva fenestrata as a platform for bio-based film production. A top-down approach was developed to remove cytosolic components while preserving the native hierarchical architecture. By combining chemical and mechanical treatments, it was shown that the addition of surfactant and mechanical treatment improved decellularization efficiency and scaffold integrity. The surfactant Cocamidopropyl betaine (CAPB) increased pigment extraction threefold during solvent treatment. Combined with ultrasonication, a synergistic effect enabled high extraction efficiency at solvent concentrations as low as 5-10 % and accelerated kinetics to equilibrium within 180 min. Auger-based mechanical pretreatment further enhanced extraction by promoting pigment removal before solvent-surfactant treatment. Biopolymer anatomy mapping by optotracing with fluorescent reporter molecules showed tissue-dependent recovery: In blade tissue, thinner-walled regions were more affected, whereas thicker-walled tissues retained integrity through an intermediate lamella. In rhizoidal tissue, fibrils from the median layer were additionally isolated. In both tissues, impairment of the outermost layer enhanced decellularization efficiency. Carbotrace 680 stained blade cell walls, while rhizoidal cell walls required Carbotrace 630, highlighting compositional differences. Fully algae-derived, self-standing films from decellularized Ulva were produced, reaching tensile strengths up to 39.7 MPa. Blade-derived films showed the highest performance, while rhizoidal films were more heterogeneous due to fibril inclusion. This demonstrates decellularization as a sustainable, low-input route to utilize macroalgal architectures for bio-based material development.