I continued with the nigiri. The Japanese chef suggested the samba, a cured silvery fish—new to me and so I went for it. It was characterless. By the way, I can’t find any information on it online. Our guy insisted it wasn’t regular saba (mackerel) and it didn’t look or taste like it. It’s possible I misheard the name but I did ask the guy to spell it.
Addendum: I am told that this is in fact “sanma” or Pacific saury.
Sanma sushi or sashimi is a little weird even in Japan, but it is lovely broiled in autumn.