Extremely long nanofibers, whose lengths reach the millimeter regime, are generated via co‐aggregation of a melamine‐appended perylene bisimide semiconductor and a substituted cyanurate, both of which are ditopic triple‐hydrogen‐bonding building blocks; they co‐aggregate in an unexpected stoichiometrically mismatched 1:2 ratio. Various microscopic and X‐ray diffraction studies suggest that hydrogen‐bonded polymeric chains are formed along the long axis of the nanofibers by the 1:2 complexation of the two components, which further stack along the short axis of the nanofibers. The photocarrier generation mechanism in the nanofibers is investigated by time‐of‐flight (TOF) experiments under electric and magnetic fields, revealing the birth and efficient recombination of singlet geminate electron–hole pairs. Flash‐photolysis time‐resolved microwave conductivity (FP‐TRMC) measurements revealed intrinsic 1D electron mobilities up to 0.6 cm2 V−1 s−1 within nanofibers.