Although the Japanese have extensively migrated to western South America (Chile and Peru), Japan is much closer to Spain (6700 miles, 10800 km) than to Argentina (11,000 mi or 17,700 km).
This is mainly due to the width of the Pacific Ocean, which conversely makes travel to South America more direct. Also, flights from Japan to Spain could use the trans-polar route north of Russia, making it even closer.
Japan and Spain are both centered near 40° N latitude, while Argentina is at least 22° south of the equator.