I have found an ingenious way around the "Guardian". By using a Cyborg Demon as a direct link, I can teleport a massive amount of energy directly to the surface. It is possible that overuse of this technique will attract its attention, but that bridge can be burned later.

Annoying that this is something I even have to consider, but nothing I have come up with has been able to affect that thing in any away.

It is wryly amusing that Humans, as a whole, have no concept that the only thing standing between them and the entirety of demonkind is (as far as I can ascertain) a near brainless energy weapon.

Ah well. I've used the last few hundred years to good effect. 

-Notes by the Demon Master, The Head Master, collected by the Demon Master Bael