This Mysterious Power is the one who captured or imprisoned Blaster Blade, Blaster Dark, and Dragonic Overlord. Before these units were captured, Aqua Force was also captured a long time ago. But Leon Soryu made a contract with Void to release this clan by sacrificing the Royal Paladin, Shadow Paladin, and Kagero clans.
The definition of Void by Takuto Tatsunagi is, "A thing that doesn't have a physical form, existing only as a will and its power is immeasureable....."
In Season 3 a new enemy named "Reverse" appears. Reverse is the avatar of Void once again attempting to destroy Cray and Earth due to both worlds overflowing with life, according to the agent of Void that possessed Takuto Tatsunagi. This is also supported by the creation of Hollow Twin Blades, Binary Star and Binary Star Twin Gunner who were created with data from Blaster Blade, Blaster Dark, and Dragonic Overlord who had been sealed by Void. Then, the Reverse created Link Joker units, who has the abillity, "Lock".
It is later revealed that Schwarzschild Dragon of Link Joker was responsible for the sealing of Blaster Blade, Blaster Dark, and Dragonic Overlord, and as a result of this is also responsible for the War of Liberation.