Over 2 centuries ago after the the tap trio becomes unfused a mysterious portal came to the world out of nowhere, a ferocious intimidating, dragon appeared out of it, we now know as Rezerem, Arceus created it to watch over the tao trio making sure they are safe, but it wasnt like that, rezerem was sent to protect but some dark magic, went into its mind, making it into the opposite of protecting. Using it's powers it summoned the tao trio, zekrom, kyruem and reshiram standed in front, but then poof!, rezerems arm went through zekroms chest as zekrom was trying to welcome it, tearing it's power out weakening it alot, reshiram and kyurem see this and go in for attack, it was a massive war despite it being a 2 v 1 the two fall to rezerem, while the dragons are on the floor dying, the rezerem takes the souls out of reshiram and kyurem, creating two new pokemon, the firewillpower from reshirams soul created flarius, and the cold alabaster strength from kyrurem creates shivrius, we know these three as the ferocious beasts. The 3 dragons vanished, meanwhile the 3 tao dragons sadly lost there lives and have never been seen again.
Well, 1 century later. Arceus finally sees what has happened to the 3 dragons, he is shocked at his creation, rezerem was a mistake to make
So Arceus decides to give the tao trio another chance, so Arceus purifies all of there souls, well accept 1, Arceus accidentally purified kyurems soul to be just like Rezerems. After that happens, the 3 dragons flew away to now this time never to be seen again.
Till black and white...
Let me know if u want me to make this a series I thought of this idea and I think it is very interesting