Japan was a closed country for most of the Tokugawa shogunate, having very limited contact with outsiders. After Commodore Perry's arrival and the forced end of the closed country policy, did Japan suffer introduced diseases from contact with the outside world?
I could imagine Japan suffering much like the Aztecs did, with Eurasian plagues striking that they were isolated from before. But I could also imagine that those plagues remained endemic in the Japanese population throughout the whole closed period, so reopening contact didn't introduce much new.
There were outbreaks of diseases that could be traced to the open of ports in the late Edo. However, the very lively and active trading port of Nagasaki seem to have been enough to regularly introduce diseases to Japan, demonstrated by the first outbreak of cholera taking place a long time before Perry's expedition, meaning they were never as isolated from Eurasian diseases as the Americas pre-colonization. See here and here by /u/y_sengaku.
Also note that it is a myth that diseases decimated the native population of the Americas before conquest and colonization, like a certain someone who says that it was the the decimation of native population that made conquest possible. In reality, most of the conquest of the Americas were done by the native Americans themselves. The diseases only decimated the population after and in conjunction with brutal conquest and colonial policies that greatly disrupted the traditional socio-economic networks of the region and thereby also decreased physical immunity of the people to fight off the diseases. See here by u/Kochenvnik81 and /u/anthropology_nerd. Such brutal policies weren't implemented in 19th century Japan because they weren't conquered and colonized.