"Under Japanese law, the operator has sole liability; designer and builders have none."

Under most legal systems this would be the case initially. The operator has a contract with the user... obvious. However, there USUALLY would be "further" liability as the operator (owner) would usually have recourse against the designers and builders as they had a contract for the design and construction which would include not fucking over the world, whether stated specifically in the contract or simply implied in the nature of due diligence. I realize that is not quite in proper legal terminology but, in engineering terminology, the designers and builders are fucked although it will take many years for the owner to fuck them. But, they will get fucked... and they should get fucked.

I only say they should get sued severely in the spirit that it may prevent such tragedies in future. It serves no immediate gain except "revenge" but it may help to alleviate such a disaster in future.

Am I off base with that?