We report the ultrafast optical pump-probe spectroscopy measurements on the recently discovered quantum critical ferromagnet CeRh$_6$Ge$_4$. Our experimental results reveal the two-stage development of the hybridization between localized $f$ moments and conduction electrons with lowering temperature, as evidenced by (1) the presence of hybridization fluctuation for temperatures from $sim$85 K ($T^*$) to $sim$140 K ($T^dagger$), and (2) the emergence of collective hybridization below the coherence temperature, $T^*$, marked by the opening of an indirect gap of 2$Delta$ $approx$12 meV. We also observe three coherent phonon modes being softened anomalously below $T^*$, reflecting directly their coupling with the emergent coherent heavy electrons. Our findings establish the universal nature of the hybridization process in different heavy fermion systems.
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