Go to amusement park, museums, aquariums, parks, movies, cafes, Izakaya (Japanese pubs), bars, take a walk, shopping, video game, manga, anime, travel, etc. I think it is not that different from other countries. :)
Generally the locals hang around the slot machines which can be addictive besides 'wasting their money' but they can be doing away with gardening as most Japanese houses have fairly good sizes of greens to work on ! Creating a feast for family is a fast catch up !