The True Plasma Bakugan are almost extinct in Vestroia and the Human world, but many of them still reside in the sealed off section of Vestroia - the Old Vestroia, and Vestroia's small pocket dimension - Caliban.
The True Plasmas, along with the other Lost Attributes (Ice, Poison, Nature, Metal, and Lightning), were sealed off long before the Six Legendary Soldiers came to be, as a result of a bloody war between the two alliances of six attributes (also known as "The Slaughter Of Twelve")
In order to end the war and avoid the meaningless destruction of all Bakugan, a Plasma warlord named Kirin sacrificed his life to create an energy barrier between the two Attribute Alliances, thus separanting Old Vestroia from Vestroia (later New Vestroia). As a result of the separation, the balance between positive and negative energy in Vestroia became highly unstable, putting the fate of the dimension in jeopardy once again. However, with his last breath, the dying Kirin transmuted his own body into a cluster of concentrated elemental energy, which would later mold into the first Perfect Core.
Centuries later a corrupted scientist, codenamed Xenodal, created a copy of the True Plasma Attribute by extracting the attribute energy of all six attributes out of living Bakugan, fusing the attributes together and injecting the mix into White Ones (the mutated Bakugan with no attribute). His first 78 test subjects died shortly after being infused with the Pseudo-Plasma, and his first successful experiment was Test Subject # 79, a young Bakugan also known as Plasma Chimeriad, and the future Guardian Bakugan of Maria Kakuzawa. Chimeriad later deserted Xenodal's army after finding out about their true motives and after witnessing Subterra Lamia, his mother figure, nearly die as a result of being overloaded with energy during the experiments.
Pseudo-Plasmas are usually unable to evolve, however Chimeriad somehow managed to evolve out of sheer rage while battling against Baki and Asanbosam, also known as The Elite Soldiers of Xenodal's army. (Bakugan: The Xenodal Saga)