My Dullahan System

When creatures thought to be mythical suddenly begin an assault on Earth, the world's nations band together to devise a plan to counter them.

Some share information on building powerful weapons, while others provide manpower.

Unfortunately, humanity does not stand a chance against an enemy that has been hiding since ancient times.

Driven into a corner, humans retreated into Undercity, the last stronghold of the human race. Due to its location in a large underground cavern, Undercity has managed to avoid destruction. Here, civilians can live fairly normal lives, and some have forgotten about the war.

A group of scholars devised a method to mimic the abilities of mythical creatures, but learning to use them effectively and safely proved difficult, so they locked away all their research.

Theo has only his mother left and is terrified of losing her. Desperate to protect her, he dedicates all his free time to researching the scholars who founded Undercity, hoping to unearth the secrets they left behind.

One day, he finds an old rusty dagger hidden in the hollowed-out hollowed-out pages of an encyclopedia printed before the start of the war.

This dagger held many secrets, and Theo lost his head while decyphering them.

"It's time to go for a midnight walk."
"Reap a soul within 4 hours."
"Where's your head?"