In another world, there were Eight Gods -- Not Four. The Four Gods of Yang, the Four Gods of Yin- gods so old they no longer had names. However, the Sage that Created The World, Taiitsukun, was firmly aligned with Yang, and favored the Yang Gods. This displeased the Yin Gods, who ruled the Underworld and could not enter Heaven.
And so they decided to make their own sage. A prince of the Real World had found the book they created to counter the power of the Shijintenchisho. He discovered the Gods of Yang's book -- but it was the Gods of Yin who bid him to enter after he was executed for treason and black magic, and seduced him with power and promises. They took his soul and made him a God of Chaos and Disorder, just as Taiitsukun was of Balance and Law.
Unfortunately, they did not counter his own black arts--and he turned on them once he got his 'god hood'... He chose a poor people to secure a worship base to torment, and set about setting up his own thing. The take over the world thwarted, the Yin Gods banished, the Four Gods watched warily, unable to act against him directly as he bided his time...
And after a few gods were summoned, he had bled off enough of the power of the Yin Gods to make his move. Using the mentally broken young Seiryuu Seishi Nakago to make his bid for true Godhood and ruling the world himself, he set out to get Seiryuu summoned, and use the Yang god's magic to make Nakago a god--under his direction. He would be the first of his New Yin Gods.
He failed.
Nakago proved too human and too fallible. So, he decided he'd just MAKE his servants--he had already cultivated dead souls to be his soldiers, and instead made them his Shitenou -- akin to the Yin Gods, but far less powerful. They were Generals, instead of his equals.
The Shitenou proved to weak. They were beaten, and he himself sealed.
With Tenkou sealed, the powers holding the Yin gods back were broken. As the souls of the book began to progress to the real world, the Yin Gods made their moves to enter the real world... only to find they couldn't! They had to have mikos of their own to break the final seal. To allow the gods of Yin to fully enter the world they had been banished from so long ago.
Individually, they lacked this power, but together the could mange to summon one. One girl defended by seven seishi, each with powers derived from their gods. Finally, together, they could reach her and whisper promises of power, if only she'd free them.
There was only one problem. The Yin Shijintenchisho was in America being studied by a translator there. The miko they touched resided within this same city, and submitted to their seduction-became the vessel for their powers.
Now New York City has become a magnet for those of power, both for good and ill. Creatures not seen since time immemorial have been spotted by portions of the frightened populace and dismissed as 'end time' gibberish. Crime rates have risen, and law enforcement has managed to keep things barely normal.
Most importantly, the warriors of the four gods have begun to converge upon New York, their memories slowly returning as they begin the search for eachother and their mikos.