Mobile speed cameras have been approved for use in Tokyo (and will later be rolled out in the rest of Japan).
They are able to be set up by a single person, and they will mainly be targeting roads frequented by the elderly and streets near elementary schools.
Not clear yet what signage* they'll be required to use with these, and it is also unclear how tightly they'll be setting them**, so be even more attentive to your speed than usual in residential and school areas. We also do not currently know how many units they have, so it's impossible to say how prolific the cameras will be.
For motorcycles, as usual, the cameras are front-facing so it doesn't affect us as we have no front plates.
*Fixed cameras require warning signage at 2 km, 1 km, and 500 m on expressways.
**Fixed cameras are usually set at 30 over on regular roads, and 40 over on expressways