A semimetal that has extreme quantum properties. In essence, Realium is extremely real, and cannot be annihilated by any form of matter or energy in existence. However, due to the immense quantum fluctations involved in keeping Realium real, Realium does not actually exist in any universe, therefore Realium will not bond with any atoms of any form, Realium atoms included.
Realium doesn't even exist in any universe, therefore until 2032 it was deemed useless by the Multiversal Court. However, it was found in 2032 that Realium could be converted into Realion by way of the Trevors-Phalen Mass Centrosystemic Field and then bonded with Fictionium to create Fictionite in order to build starships. Realium itself is still useless.