Under the driver seat of my new Vellfire 2013 is a small rectangular blue grey box about 10x10x3 cm with a wiring connector going into the back of it and a label with B2 in big letters on the top. Does anyone else have one, or know what it is? (I would upload a photo but I get a message saying "you do not have any existing attachments" whatever that's supposed to mean!

Without seeing a picture of it, my guess is it could possibly be an ETC box, do you have a small antenna on the dash near the windscreen at all?

Under drivers seat? The only standard things would be the subwoofer (black) fitted in the 18 speaker system and the 110v inverter ( if you have the Japanese ac sockets in the rear of the centre console and the 150watt AC switch to the right of steering wheel.

Without knowing your full spec or modifications from previous owner, hard to say without a photo