Check out this Gaijin Tip from video/blogger kanadajin3, who is actually named Mira and is “a girl who moved from Toronto, Canada to Tokyo, Japan.”
Eat all your rice in Japan. Leaving food behind is rude esp if it is rice bits. When you scrape food off your rice cooker, you need to take everything, leaving little bits is ruder than leaving a lot. If you just can’t finish your food that you got at a restaurant then you can leave some behind, but try to finish everything at home and at your friends house.