Visiting Google Maps, I came across this long, sinuous, while pretty regular mark undersea that looks like an ancient river, when the sea was way lower, or a big (big!) boulder that could have rolled down to the bottom (?).
Given the location (ring of fire), it could also be a "crack" made during a major (and ancient) earthquake that, with time, has been filled with sediments.
This looks like this question, but the shape is very different, and much less sinuous than the one in Japan.