Stairs popped out after the entrance, plunging into the dark depth of the cave. The perpetual darkness of the Blackvault Mines seemed bright compared to that descending trait.

Enatsu could not hold back his trembling legs. Yoichi followed Shioko step by step, with Kenji was clinging to his leather pouch. ​​

"These stairs lead into a large circular room, located more than twenty meters deep. Once we kill the boss inside, we can finally get out of the dungeon," Shioko explained. Without getting lost in pointless chatter, the archer descended the first step of the long staircase.

As soon as the plan of her boot impacted the step, the same noise as the sticky mud that had characterized all the sound of the dungeon rumbled louder than usual.

The large circular door leading to the boss's room masked the cramped space the tamers had to travel to move to the last area of the dungeon. The staircase was located inside a descending tunnel just over a meter and a half wide.

The sludge accumulated at that point was much more abundant than all the other rooms in the mine. However, a strange physical phenomenon was taking place on those stairs: the dense mud, despite being subjected to the natural slope of the rock, climbed the stairs with an upward trajectory.

Black mud particles flowed from bottom to top, carrying debris of various kinds and small shrubs or remnants of insects and climbing vertically upstairs. They flowed out of the tunnel leading to the boss's room.

Splitting on the sides of Shioko's boot, the flow of mud overcame her foot, continuing undisturbed its path outwards of the large circular door.

"What the hell am I looking at?" Enatsu gulped, spying over the step. The merchant rubbed his eyes, believing that that vision was a hallucination due to tiredness.

"Is the mud really going up the stairs?" he continued, pale as a corpse.

"Apparently, Yoichi was right," Shioko stated in a low voice. Her second foot also dropped to the first step. "It just seems that the source of the black mud is down here," she remarked, rolling her eyes towards Yoichi.

Yoichi turned his gaze back. Half of his face was illuminated by the light of Nobu. Due to that tunnel narrower than the initial one, the bulky butterfly demon could not fly inside.

"This substance came out of the Blackvault Mines and extended to Blackborough. If we can't find a way to stop its advance, it could go north and... well, I don't even want to imagine what might happen if it reaches the capital area," Yoichi thought out loud.

The sickening smell of that dark substance had now soaked the nostrils of the three travellers, who had become immune to its stench. The mission of Hyobe's necklace, the object that had driven them to enter that dungeon, had taken second place, losing importance.

Something was using that dungeon boss's room as some factory to produce that black mud.

Nobu flapped its wings forward and put its insect paws on the shoulders of its tamer. Soon after, the Hotasagi closed its large coloured wings, bending them on its back and considerably reducing its body volume.

"Be careful. I know the next room perfectly, but something tells me that the boss we meet will not be a demon like the others," Shioko spoke. The obvious concern arising from the archer's words worried her comrades even more.

Yoichi and Enatsu, when they left Goldhaven in her company, were sure that they would complete the dungeon without any problems. Their guild leader had assured them that Shioko's ability would facilitate finding the necklace, not suspecting anything his warriors would actually face.

When the three of them began to walk through the tunnel and left the topographic surface, the sound of mud bubbles bursting joined that of their deep breaths.

The rock steps of the staircase were irregular in height, different from each other and sometimes slightly sloping. As if they were walking on a reversed waterfall, the three adventurers sank their boots in the mud, descending more and more in altitude.

After a few minutes, the air became unbreathable, saturated with carbon dioxide and other unknown gases released by the mud. Although the mud was boiling like water in a pot through some incredible chemical reaction, the temperature dropped with depth.

The deep breaths of the three guildmates condensed into water vapour, visible from their mouths. The fingertips and the tip of their noses began to lose sensitivity, as if suddenly they had teleported in a middle of a glacier.

"Brr!" Enatsu shuddered without adding anything else. The merchant grabbed both the flaps of his long coat, clutching it to himself and rubbing its fabric against his body.

Walking sometimes on all fours, sometimes on two, Rokuro followed him from behind, closing the line. In addition to the low temperature and partial anoxia, that descending section of the cave was characterized by a progressive increase in air pressure.

"This place was a mine, and the boss's room must've been the last mineral field to be excavated before the demons took control of this place," Yoichi commented, trying to give a historical meaning to that deep tunnel.

"Yes, that's right. Official documents testify that when the Tetsuiasa's richest surface deposits were exhausted, the miners dug this deep tunnel, continuing to look for minerals without compromising the stability of the mine," Shioko confirmed. With that statement, the archer proved that even a speedrunner could be knowledgeable.

Chatting in a low voice to kill the time, the three tamers continued to descend. A broad curve bent the tunnel, and a faint reddish light interrupted the darkness.

The intermittent light alerted the three warriors by reflecting on the walls of smooth rock. They slowed down the pace, realizing that that curve was what separated them from the fateful boss's room.

After a descent of more than ten minutes, they were about twenty meters deep. The dungeon's exit was far away, and even if they wanted to escape, halving the level of their demons, they wouldn't be able to travel that distance in such a short time.