In the year 20XX AD, mysterious shipwrecks have been continuing to occur near Japan. Oki Juzo and Itsuro disappears to investigate these incidents. Just before they left, they came by a key engraved with the letters "SS-99" in the underground lab where Juzou's grandchild and Itsuro's younger brother, a senior high student Oki Shinji, had been improving various "99 Shikipo…