What is the strongest shield in the world?

There was a shield made in Japan by the last surviving student of masamune. It was a round disc made from meteor fragments. The fragments were processed like tamahagane, except smelting took 1 month or 30 days to complete. The disc was folded 1,000,000 times and a perfect circle down to geometric measurement. The secret heat treatment known only to masamune and one student was used. Then the shield was expunged into an oil, perhaps clover oil... this resulted in the shield taking on a particular curve. It could withstand any blow, and send an equally opposite reaction into its source. A yakuza spy for the united states stole the shield from a top secret facility and smuggled it back to the states. There is no further knowledge on the shield or its current whereabouts.