We study MeV-scale electrophilic feebly interacting particles (FIPs), that may be abundantly produced in supernova explosions, escape the star and decay into electrons and positrons. This exotic injection of leptons in the Milky Way leaves an imprint in both photon and cosmic ray fluxes. Specifically, positrons lose energy and annihilate almost at rest with background electrons, producing photons with 511 keV energy. In addition, electrons and positrons radiate photons through bremsstrahlung emission and upscatter the low-energy galactic photon fields via the inverse Compton process generating a broad emission from x-ray to 𝛾 ray energies. Finally, electrons and positrons are directly observable in cosmic ray experiments. In order to describe the FIP-induced lepton injection in full generality, we use a model-independent parametrization which can be applied to a host of FIPs such as axionlike particles, dark photons and sterile neutrinos. Theoretical predictions are compared to experimental data to robustly constrain FIP-electron interactions with an innovative multimessenger analysis.