I don't believe that most people in Japan have any awareness of 'what happened in Italy'. And what in particular did happen in Italy? Apart from a brief flurry of interest in Turin during the 2006 as a background to Japan's Winter Olympic medal hopes and lots of very dramatic reporting of the deaths during the peak of the coronavirus outbreak (complete with a horror film-type soundtrack), I've seen almost no coverage of the country in the Japanese media beyond the 'Isn't Venice pretty?' and "Isn't pizza delicious?' variety. And I've never noticed any greater aversion to foreigners among elderly people compared with younger people since coming to Japan in 2003. All this is anecdotal I know, but one thing that is factual is that Japan has not experienced vast global migration as you claim. The number of foreigners is still only about 2.5% of the population, up from about 1.5% when I first came here. And we're not particularly conspicuous, apart from in a few areas.
I agree with you that coronavirus is exposing various faultlines. I think that by far the biggest faultline is the massive global inequality of income, health, and job security, which coronavirus does seem to be exacerbating. However, I suspect that plenty of people in charge are going to play the migration/race card to try and distract people from this, and often their poor handling of the pandemic, to stoke their fear of the 'other', which I also agree exists.
"...very dramatic reporting of the deaths during the peak of the coronavirus outbreak..." is what happened in Italy. The sensational nature of the media report do it is what will stick in people's mind, and enough to fuel their fear. And this was due in part to many Italian's insistence on continuing normal close-contact social gatherings and activities, including many elderly, who comprised the majority of Covid deaths. Deaths that may have been preventable if not for an overwhelmed local healthcare system.
"Vast" is a subjective term, which will differ based on individual perception, experiences, situations, and tolerance level. Regardless of objective statistics. the impact will be felt more in a small, very ethnically and culturally homogeneous country such as Japan, than say, Malaysia. Especially given the Japanese culture for law, order, etiquette, cleanliness, and other social norms, behavior and general personality traits which may be very different from some of the incoming cultures. But these peculiar traits are what makes Japan Japan, enabled it to make remarkable achievements in various fields, become a developed nation, and draws people to visit or live there because of it.
Given the human propensity to view the 'other' with at least caution, if not outright hostility, foreigners will stand out if their behavior conflicts with the native's, even if it occurs infrequently or among a minority. Until trust is established and a base level of compatibility is reached among the native and incoming group, then the tendency is to paint the incoming group with a broad brush and view them with distrust, or anger if they are perceived to lower the native's standard of living in any way. At the societal level, this can only occur organically over time, I'd say at least a generation or two.
Rapid demographic changes - especially among visually different groups (races) and/or vastly different cultures - that occur before that leads to reactions and conflicts we are currently witnessing worldwide, with the rise of nativist parties and movements from Britain, to the US, to Germany and France, and other Western European countries. This is worsened if the government does not encourage assimilation, which builds trust amongst diverse groups and lessens the negative effects of the tendency to 'other' the incoming group. Media PR, educational programs, etc praising just the benefits of diversity alone doesn't cut it if the local on the street sees and experiences otherwise. And ignoring, denigrating, and attacking the natives' oftentimes legitimate concerns and very real experiences will turn potential allies/friends into foes/enemies, by increasing local support for nationalistic parties. And everyone will lose, both natives and the incoming group(s).
Natives who tolerate it just for the financial benefits will quickly turn against it if the economy tanks. Then the base survival instinct to compete for resources will dominate and the foreigner- the 'other' - is now viewed as just a competitor for scarce resources.
I don't live in Japan, nor am I knowledgeable enough about its domestic immigration issues to comment of the specifics of your situation. These are my opinions on a global phenomena, by someone who has been both native and incoming, and witnessed the effects - positive and negative - of the changes within my adult lifetime, in various countries)
