What had happened

Back in the beginning of 2020 February mankind had lost hope ,life its self was in ruins buildings destroyed so humans survived by living in the ocean for 300 years. But as life continued we gathered more data on the DD-20 a human eating organism. After the DD-20 was found mankind tried everything to destroy them but they could only gather evidence on the source of the DD-20. It was a virus that evolved at a rapid pace when came into contact with a unknown metal found in the Arctic after light had made contact. The metal was just a normal metal from space, scientists believe the metal was contaminated with a specific radiation only found in space and. Five years later America and Japan joined forces and studied the metal they melted it into bullets that soon failed spears ,knifes and others failed against the DD-20 a 7 foot skinny humanoid being until a Katana worked after that Japan and America we're only able to make around 1000 and and only those were able to destroy the DD-20After mankind went into hiding the only countries left where Japan America South Korea Mexico and Russia but after five years Russia was non responsive. Japan and American went back on land to study the dormant DD-20 after testing the katana the DD-20 was eliminate and soon children were trained to fight the DD-20 and thanks to science mankind has a chance