Comment by Gob Silaer on Seraph Of The End - Vol.4 Chapter 15: Complicated Connection

So mc has power of angels and that's what that form was it was created by an organisation which owned the orphanage and the other kids had experiments on them too but the demon army activated his power and I am pretty sure g** or whatever was angry by humans experiments and punished them by realeseing the disease and the monsters and the vampires came out of hiding and took over 
The disease can also be manipulated into becoming an angel thing or atleast glass sister atleast that what happened in the anime
Mc is a seraphim (the highest level of angel serving g** directly) atleast that my assumption
I dont know much for sure yet