Imbalanced Alfvénic turbulence is a universal process playing a crucial role in energy transfer in space, astronomy, and laboratory plasmas. A fundamental and long-lasting question about imbalanced Alfvénic turbulence is how and through which mechanism the energy transfers between scales. To solve this problem, we successfully decompose and trace the dynamics of interacting fluctuations and find that along the energy cascade, the collisions between counter-propagating waves transform into the interactions between co-propagating waves and structures. We also reveal that the energy transfer of waves and structures is carried out mainly through local-scale and large-scale nonlinear interactions, respectively, responsible for their bifurcated power-law spectra. This work unveils the essential energy transfer physics of imbalanced Alfvénic turbulence, explains recent observations from the Parker Solar Probe in the inner heliosphere, and revises the traditional understanding of imbalanced Alfvénic turbulence that invokes counter-propagating waves.