Hi Nick, this is a cutout of Earthquake Emergency postcard, 1 1/2 Sen blue, issued Nov 15, 1923 (Japan Specialized Stamp Catalogue PC27). The perforation seems to be crudely applied by scissors or something akin to make it look like a postage stamp... no way anyone could be fooled.
I only possess the reply-paid version (PC28, in red-brown) with identical design and cancellation, which shall give you a good idea how the original entire postcard should look like.
Hope this helps.
Cheers, from Hironobu