Osgard is a parallel dimension above the mortal world and home to a highly advanced race named Osgardian. The old prophecy says that Hader, the Lord of the Netherworld, will massively invade Osgard with the four Nether Commanders, Minos, Lucis, Karura, and Pando. The twilight of Osgard is falling.

As followers of Osgard spirit, Thunderstrikers joined the final war but found a slight advantage against the overwhelming Nether forces. To defend Osgard from destruction, Athena led Thunderstrikers to the Forbidden Pool to prove themselves worthy of the mighty thunder power.