The ‘tunnel’ was a special ability of Aleister that helped undead monsters hide underground and ambush when he needed them to.

That’s right... Aleister was extremely good at fighting through ambushing, using these tunnels of his.

Kang Chul-In remembered the time when he was allied with Aleister.

During the time when Kang Chul-In’s Ishtar Coalition fought against Vilhelm’s Gullveig Alliance on the Monocork plains, Aleister had completely wiped out four of the enemy's divisions using the tunnels. 

“Then… you’re saying that on the way to the 18 peaks, undead monsters are waiting underground?”

“There’s an extremely high possibility of that.”

“Then…”

“First, we take care of them.” Kang Chul-In said, pointing at the picture taken by the Cosmic Force.

“The enemies don’t know that we’re here. Looking at them setting up right now, they probably weren’t aware of our marching speed.”

“Y-Yes, sir.” Kwak-Jung agreed with...