User blog comment:Godisme/Magical Barrier Particles/@comment-1359322-20131031161651/@comment-5668006-20131101021912

I'm pretty sure that E.N.D. is the only book and his/her/it's power is to spawn other demons which is what would make it such a scary foe. With that being said, the 9 demon gates may be able to constantly spawn as long as E.N.D. exists which is why Igneel wanted to destroy it. This isn't the only demon that has existed but it 1 hasnt shown itself 2 igneel hadnt tried to destroy any others possibly because like i mentioned it creates other demons.