http://www.japantoday.com/mobile/view/law-requiring-backseat-passengers-to-wear-seatbelts-takes-effect

Finally, a law that people must wear seatbelts in the back seat. And it will ensure that taxis have to make the seatbelt accessible too! I also liked the addition about urging cyclists not to use mobile phones or umbrellas when they are ride. This is something that struck me when first visiting Japan, I haven't seen people doing this in any other country...