After the initial observation of neutrino oscillations using atmospheric neutrinos, considerable progress has been made in the understanding of the mixing paradigm using long-baseline and reactor neutrinos. Despite these successes, there are several open questions remaining, including the ordering of the neutrino masses, the octant of the atmospheric mixing angle, and whether or not neutrino oscillations violate CP. Hyper-Kamiokande is next-generation water Cherenkov experiment that will observe long-baseline neutrinos from J-PARC as well as atmospheric neutrinos with its 187~kton fiducial volume. While its atmospheric sample is subject to considerable matter effects and provides sensitivity primarily to the neutrino mass hierarchy, its accelerator neutrino sample provides a clean measurement of the CP phase in the PMNS mixing framework, especially when the hierarchy is known.
This talk will discuss Hyper-Kamiokande's oscillation sensitivity using atmospheric neutrinos and demonstrate the power of their combination with the beam sample to realize early resolutions to the open questions in oscillation physics.