Hyper-Kamiokande (Hyper-K) is the next upgrade of the currently operating Super-Kamiokande experiment. Hyper-K is a large water Cherenkov detector with a fiducial volume which will be approximately 10 times larger than its precursor. Its broad physics program includes neutrinos from astronomical sources, nucleon decay, with the main focus the determination of leptonic CP violation.
To detect the weak Cherenkov light generated by neutrino interactions or proton decay, the employment of the multi-PMT concept, first introduced in the KM3NeT detector, is considered as a possible solution. A multi-PMT Optical Module - a pressure vessel instrumented with multiple small diameter photosensors, readout electronics and all required power supplies (incl. high voltage) - offers several advantages, such as weaker sensitivity to Earth's magnetic field, increased granularity and directional information with an almost isotropic field of view. In this contribution the development of a multi-PMT module for Hyper-K is