What does this switch do?

welcome!
your pic isn't working, and we don't get that in n/a. hopefully, someone with a jdm will chime in.

all the best!

 

I believe the only rocker switch that would be expected in that area would be for the left/right mirror adjustment switch, so if it's not that I suspect something aftermarket - but without the picture we can only guess.

 

Nothing a little URL-foo can't fix



The dash dimmer only has an effect when the headlights are on. DRLs can be on and the dimmer won't adjust anything.

The ♪ button turns off the low-speed noisemaker. There's a video about it here, which ironically is in Japanese and was uploaded to the PriusChat channel.

And I'm curious what that thing is just above the hood release.

 

Have you tried asking it to open the pod bay doors?

 

The pictorial index in the Owner’s Manual (PDF, in Japanese) shows the headlamp cleaner switch or the manual headlight beam axis adjustment dial in that position. Neither of those controls (shown on pages 293 and 307) looks like yours, however, so I agree with @QuantumFireball: it’s probably an aftermarket installation.

If the switch has both left-right and up-down controls, perhaps it’s the target designator.

It’s an onboard unit for the electronic toll collection (ETC) system used in Japan. If you were in Japan and had an ETC smart card, you’d insert it there to pay for expressway tolls automatically.