Soundproof jar you can scream into to let off stress. From a list of 101 products only available in Japan. I also like the soundproof karaoke machine, which lets you sing into a funnel microphone without anyone else hearing you.
I've only looked at 20 products so far but there are probably more can't-live-without Japanese inventions on the list.
Product descriptions with pix, year of invention, and price in USD at Investing.com.