Wow! So a little seawall would have done nothing to this. Even if the nuclear plant had a 10 m seawall, the water would have just jumped it. I think you have to put the backup generators on top of rugged buildings.
But get this! This is not the record holder! There was a higher tsunami. Now that the M9 has shot its load, they should not worry about big tsunamis on that coast, but go to the other areas.