fantastic plot, i do hope you are adding to this soon i am anxious to see what happens :) (r&r some of my stuff if youd like :))

'The invisible veil that separates the human world, and the world of shadows, _were_ the creatures of nightmares dwell, ripped.'- I assume you meant WHERE.

'...entering the human world and reeking untold amounts of havoc.' - Unless you really do mean that the havoc smelled, the word is 'wreak'. A spell check will not insure that you use the right word; it will only make sure that the wrong word is spelled correctly. Also, lose 'amount'. '...wreaking untold havoc.'

'...between the demons and there halfbreed offspring...' Homophones, words that have different meanings but are pronounced alike, can be very confusing. Their, there, and they're all sound alike. In the immediately quote above, THEIR is the correct word.

They were indebted to them to forever be the guardians of mankind - These pronouns need antecedents. I can't tell to whom the They and the Them refer.

Until 2012, when the last remaining Toren left, and went into hiding. - This is a sentence fragment. Try: 'The last Toren left in 2012.'

'...they slowly became killed one by one...' Try this: '..they were killed one by one...' or '...they died one by one...'

As currently written, it seems that the first angel/human mating occurred in 20. Why then? Did something change? If so, what?