Method, Law
Tsunamis in the past changed the methods and laws of today.
Tsunamis used to come crashing into towns, just leveling them completely. Today we have new methods of building and protecting ourselves, and laws to keep them in place, so the past doesn't repeat itself.
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These methods and laws affected your own home (ほう) the most.
Your home has strong walls and ceilings. You aren't allowed to leave the doors unlocked and open. These methods and laws are because of those past tsunamis and the damage they used to cause. Your home is safe thanks to them!