The Geospatial Information Authority of Japan (GSI) started to provide national tiled maps in 2012. Initially we could not use the tiled maps with GDAL TMS minidriver because the tile URL naming system was special.
Almost one year later, GSI adopted a common tile map system known as slippy map or XYZ tile, which is used by major web map services such as Google Maps and OSM, and released GSI Tiles officially. Since then we can access the tiled maps via GDAL TMS minidriver, but I am not satisfied with some points - incorrect displayed image (I'm not sure it's because of mixed image format. This problem might have been resolved now), image quality and no reaction with high CPU usage while fetching data. So I shared TileLayerPlugin in the QGIS plugin repository.
Last May, GSI started to provide WMTS metadata for the tiled maps experimentally. The quality of image data from the QGIS core WMTS provider is high on both map canvas and print, and there are many rendering options in the raster properties dialog. I can do what I want to do without the plugin.
If there is a similar WMTS service (metadata) for OpenStreetMap, we can use the maps via the WMTS provider. Does anyone know if there is an OSM WMTS service?