The end of an arc!!! I was confused the entire time!!

Everyone makes it to the airport but then the lieutenant general of the demon army shows up and starts yapping about the seraph of the end project that is an ultimate weapon made to destroy the vampires.

That entire chain of events was legit so confusing to me. It was so choppy and wild and I couldn't make sense of the battle?? So many people die and I feel like the seraph of the end wasn't even actually explained.