In terms of fatality, the Diamond Princess cruise ship [1] has the helpful property that everyone on board was tested. Nobody recovering/asymptomatic not getting tested, nobody being refused a test.

The wikipedia page lists 700 infections and 7 deaths.

Of course there are still certain biases: on one hand it happened early, when hospitals weren't overloaded; on the other, cruise ships tend to have more older people. And as I don't speak Japanese I haven't traced those numbers to primary sources.

[1] https://en.wikipedia.org/wiki/2020_coronavirus_outbreak_on_c...