Maybe look at the various input settings on your TV to see if it detects your DS?

It’s an official accessory that the DS detects no problem. It also receives tv signals, not emits.

The VCR needs to be plugged into an antenna (coaxial) or RCA (yellow, white, red), it can't just be picked up over the air unfortunately

I plugged the vcr into the tuner via the External Antenna port. So it might be something else

Otherwise I'm just gonna have to guess it's the VCR or the DS' software problem (I'm pretty sure the DS TV Tuner is a Japanese product and the US and Japan use separate video formats that aren't interchangeable)

You probably already know this, but you might want to make sure you are not trying to connect the tuner's antenna port to any of your VCR's colored outputs. The Yellow-Red-White connectors are for video and audio signals, but antenna ports require RF signals.

The only connector on a VCR that is normally compatible with a tuner's antenna port, is the RF-Out connector. That's usually a non-colored, threaded connector.