Japan is an insular, rigid and heavily values oriented society. Overall their crime rate is exceptionally low.
It would be hard to apply Japanese policing styles to fundamentally different societies. That doesn't mean we can't learn good lessons from them, but we need to remember it's never an apples to apples comparison.
(edit... sorry, don't know how this turned into a long rant. Started typing over lunch and just couldn't stop... feel free to skip this, just a stream-of-consciousness dump.)
Somewhere between Japanese idiosyncrasies and American exceptionalism, we could learn a lot from other developed societies. We just don't, because we're arrogant, ignorant, and proudly so. We mask our social ills with flags and nationalism, even though there's hardly a cohesive America left to be proud about.
IMO this isn't some academic problem like fusion, but a problem of people and politics. Speaking of values, there's a good values overlap between the police, the military, Scouting, religion, gun culture, and conservative politics & politicians. All are hierarchical, patriarchal, heavily focused on in-group loyalty and proud displays of status and power. It's a self-reinforcing good-ol-boys network that's fighting back against cultural extinction. The thin blue line, the whatever %ers, the MAGA folks... all are part of the same general in-group. To them they are the only legitimate America, and everyone else is an outsider, intruder, imposter, hellbent on destroying everything they hold dear. They don't want a multicultural America; multi-ETHNIC might be OK, but only if they fall in line and know their place.
This is not really about the tactics of policing, or training, or body cameras, but about people whose identities rely on power, status, and tradition rather than collective well-being and social innovation.
Japan is on the other side of that spectrum of collectivity. Japan is lucky (in this context) in that they are also overwhelmingly homogenous, so there isn't much of a outgroup to rebel against. They have plenty of social problems but militarized policing isn't one of them.
To the Western world, aside from its bleeding-edge aesthetics, Japanese society is heavily hierarchical, traditional, patriarchal, conservative, orderly... similar to the good-ol-boys we have here, except there, there isn't really much of a challenge to that power structure. There's no Japanese BLM equivalent to put that in sharp contrast with other elements of their society (which exist only on the fringe).
American culture, in contrast, has largely moved on (by % of population) from the good-ol-boys lifestyle, but those elements in our society are still there, and still clinging on, and hold a disproportionate amount of political power and an overwhelming amount of the firepower. Everyday, centrist Americans without significant exposure to violence and crime tend to be more welcoming of outsiders than the conservative elements, but can be easily swayed in both directions by political propaganda.
Long ago the movements veered from discussions about tactical reform and into basically mass marketing with gospel-like, life-or-death overtones and tidy slogans and us-vs-them mentalities. There's no coming back from that... you can go from "police reform" to "culture war", but it's much harder to de-escalate from that and ask about, "Wait, wait, instead of getting rid of police officers, what if we provided community specialists alongside them..."
Trump purposely escalated it into a us-vs-them thing, all the time, everywhere, across any divide he was able to weaponize, because it suited his campaign. We now pay the costs, as a society, with Biden sitting as a lame duck in the middle of it all, begging people to listen to him and be reasonable... but nobody does anymore. There's no one America anymore, just warring factions bound by a shared economy but no shared values.
shrug
Fundamentally a country this heterogenous is difficult if not impossible to govern. Maybe a EU-style model with more local autonomy would be more appropriate than federalism with supremacy. Our real flags now are either black, white, and blue or rainbow-colored, and the ol' stars and stripes are just hanging in tatters in the no man's land between them. Why not just acknowledge the reality and secede into more autonomous, culturally compatible regions and stop fight each other? There's room enough in the world for different societies & values systems, but not if they are forced by external factors to live by the same set of values against their consciences.
It would be hard to apply Japanese policing styles to fundamentally different societies. That doesn't mean we can't learn good lessons from them, but we need to remember it's never an apples to apples comparison.