In this contribution, we report a novel strategy for the synthesis of nanocrystal-containing magnetoceramics with an ultralow hysteresis loss by the pyrolysis of commercial polysilazane cross-linked with a functional metallopolymer possessing hyperbranched topology. The usage of hyperbranched polyferrocenylcarbosilane offers either enhanced ceramic yield or magnetic functionality of pyrolyzed ceramics. The ceramic yield was enhanced accompanied by a decreased evolution of hydrocarbons and NH3 because of the cross-linking of precursors and the hyperbranched cross-linker. The nucleation of Fe5Si3 from the reaction of iron atoms with Si-C-N amorphous phase promoted the formation of α-Si3N4 and SiC crystals. After annealing at 1300 °C, stable Fe3Si crystals were generated from the transformation of the metastable Fe5Si3 phase. The nanocrystal-containing ceramics showed good ferromagnetism with an ultralow (close to 0) hysteresis loss. This method is convenient for the generation of tunable functional ceramics using a commercial polymeric precursor cross-linked by a metallopolymer with a designed topology.