So in the old days when people couldn't keep fish fresh for long, they
would marinate it so it would last a little longer. Some purists to
this day don't like this idea and is considered a waste of fish
(especially some restaurants who take some high grade tuna and give it
the marinated or "zuke" (zoo keh) treatment.

I've had fantastic maguro (even chu-toro) zuke in Japan and quite good
versions in the SF Bay Area.

I was curious what ingredients, other than soy sauce and a few other
obvious ones, go into the marination? What makes one version taste
better than another?