"The great wizard Sar-Elam, know as the ‘Seventh Dragon’, sacrifices himself to end the Wars and repel the demon incursion. Sar-Elam and his disciples seal the demons away to prevent their return."
How can Sar-Elam sacrifice himself, then go and seal the demons away???
I think that this is just a clumsy translation. Here's probably what the author intended: "Sar-Elam sealed the demons away, sacrificing himself in the process for the purpose of repelling the demon incursion."
or something like that. I probably would have added a little bit more to make it even clearer