This work delves deep into the exploration of Rare-earth (RE) replacement doping germanene monolayers, where RE elements stand out for their fascinating electronic and magnetic nature derived from the elusive f-orbitals. Employing density functional theory (DFT) calculations, we unveil the electronic and magnetic characteristics of doped germanene systems. With its two-dimensional honeycomb structure, germanene holds immense promise for a wide range of applications within group IV materials. Through the discussion, we deeply uncover how the substitution of two specific concentrations of RE-atoms, namely La, Ce, Pr, Nd, Sm and Pm, transforms semi-metallic non magnetic germanene to half-metallic ferromagnets with remarkably high critical temperatures, when Hubbard correction is considered. These revelations not only deepen our comprehension of integrating f-orbitals into germanene but also open up exciting avenues for advancements in spintronic devices and beyond.