Ben decided to let Mira fight the 3 Etherious first. She was pissed off with them, because they were the ones who sent those annoying small fries. Ben had his fun though, so he liked them a bit.
Mira transformed into her Satan Soul form and rushed towards the adult female, Zoe first. Some weak Etherious appeared in front of Zoe to block her. She easily ripped their bodies apart, killing them.
Zoe was panicking and ran away, so Mira pursued her. Then some beetles attack Mira. Neo, the teen male Etherious has released all the beetles inside the transparent eggs. They all attack Mira and they can withstand her physical attacks.
"Annoying bugs." Mira said as she created a big, dark orb.
She fired many dark bullets at the bugs and destroyed them. Neo was becoming panicked too and ran to the old man alongside Zoe. Both of them weren't the best when it came to fighting, so they retreat after seeing Mira destroy their troops easily.
The old man sighs and then he puts his hands on the ground. Suddenly, the floor in front of Mira moved and a lot of metal spikes shot out of it. Mira jumps to evade them, but then a lot of longer spikes come out of the ceiling, trapping her between them.
She didn't have time to evade so Ben moves to save her. He flashes and catches her, then he broke all the spikes with his gravity magic. Mira sighed because now Ben will take over the battle after she needed to be rescued.
Ben grinned as he flashed over to the 3 Etherious, while Mira flies back. He appears between Neo and Zoe who hid behind the old man. He grabbed their heads and burned them with the red solar energy produced by his Sun Devil Slayer Magic, which killed them instantly.
The old man's eyes widened as he turned around, only to be grabbed by the neck by Ben. Ben lifts him up as the man struggles to free himself from Ben's grasp. But he is too weak to even make Ben's hands move.
The old man tries to use his curse to attack Ben. Some metal pipes suddenly appear on the ceiling and they release a massive amount of flame. The flame only affected Ben though, the old man wasn't affected at all.
He smirked, but then that smirk vanished when the flame disappeared. Ben hadn't taken any damage. Furthermore, he sucked up all the flames and replenished some of the magic power he used up before.
"Using flames against a Sun Devil Slayer like me. What a foolish move." Ben said with a smirk.
The old man was surprised when he heard that. "I know that you are immune to flame. But I thought it only applied to magic, not Curses like what I used. Wait! Don't tell me you can use Curses too."
Now Ben was confused. "I have learned about it, but I can't really use it yet. Besides, even if I can use Curses, I won't be immune to it, right?"
The old man was confused as well, but he can't think about that now. He is still being held by Ben and can't free himself. Ben also doesn't want to think about it for now, so he immediately killed the old man using the red solar energy produced by his Sun Devil Slayer Magic.
"Job's done. Time to go home." Ben said as he wiped the ash off his hands.
"Has this really ended?" Mira asked.
Ben nodded and said, "Surely-"
"Not." The old man replied, but only his voice was heard, while he is nowhere to be seen.
Ben and Mira become alert and look around to try and find the old man. But no matter where they look, he is nowhere to be found. Fortunately, the old man is stupid enough to reveal his position, just like how he explained the other 2 Etherious' Curses before.
"Ha ha ha, where are you looking at? I am here, around you. I am this place itself. I am the dungeon." The old man said.
The 2 want to ask what nonsense the old man was saying. They got a answer before they could even ask. The room suddenly got smaller and smaller, as if it wants to crush them. Now they understand that the old Etherious is the dungeon itself.
"Ha ha ha, after that damn witch sealed us in this place I merged myself with this dungeon. She made a mistake by leaving our leader half-dead. It gave me the chance to devour him and gain control of this dungeon. Now I can control this place as I wish, not just setting up traps. This whole place is under my rule, HA HA HA." The old Etherious laughed manically.
"Woah, so you have 2 kinds of Curses now? And leader? So he was a lot stronger than the 3 of you?" Ben asked without a ounce of fear in his voice, just pure curiosity.
"That's right. I have the Curse of Traps and the Curse of Transmutation. Our leader was very strong, he must be the strongest one after E.N.D, HA HA HA." The old Etherious happily explained.
"I don't know who this E.N.D is, so I can't judge how strong your boss is. But I can say that he is pretty strong. Also, the only way to defeat you is by destroying this whole place, right?" Ben asked again.
"You are very ignorant to not know about E.N.D, he is the strongest Etherious that lord Zeref ever created. But you are still smarter than I thought because you are aware of the method to defeat me." The old Etherious said.
"Well, I can always find out about this E.N.D later, so it's not a problem. Although you're as stupid as expected. Confirming the weakness your opponent uncovered is not a good move." Ben said with a smirk.
"Humph, it won't change anything because you can't do anything about it." The old Etherious said smugly.
"Let's find out, shall we?" Ben asked before teleporting Mira outside.
Ben suddenly covered his entire body with red solar energy. He doesn't hold his power back anymore and released all his Sun Devil Slayer Magic's power. The room becomes very bright and hot in an instant.
The area around Ben starts to melt because of the heat that he generated. In a short amount of time, the heat also spread to the other rooms. All the remaining Etherious that hadn't been killed by either Ben or Mira now die because of the heat that caused them to dry up and melted their bodies.
The old Etherious who has merged with the dungeon also suffered a lot because the place is melting now. All the hard walls, floors, ceilings and everything there is melting because of the super high temperature that Ben generated.
Ben had become a miniature red sun that ate away at everything around him. With his current power level, Ben could melt this whole mountain if he went all out. But he limits himself to just melting this dungeon without destroying the mountain itself.
His control over his magic is really good, so he can make that possible. Still, the heat wave will spread to the surrounding area. It even came out of the dungeon, forcing Mira who had been teleported outside to get away from the entrance.
A few minutes later, the heat stopped increasing, so Mira knew that Ben had completed their job. Then the heat started to disappear and the temperature returned to normal. Ben removed the heat after making sure that every Etherious in this place had been obliterated, including the old Etherious that has become the dungeon itself.
His Sun Devil Slayer Magic had been powered up significantly after slaying all these artificial demons. He can even feel a strange change, but he can't check it out now. It's not the best time to do that because the dungeon will collapse, so he teleported out of it and then the dungeon collapsed after he left.
Outside the dungeon, Mira is standing there with her arms spread out and her eyes are closed. Ben can see many souls entering her body. Those are the souls of the dead Etherious and she absorbs them all.
She was done after a minute and Ben can feel her magic power increase. He asked her if she obtained a new form, but she didn't. Her magic had only been strengthened like Ben's, but that's good enough because that means all of her abilities have increased.
Ben and Mira were satisfied with the result of this job and they can go home now. The Decade Quest was better than they thought, although it might be because they're compatible with this job. They want to go on another one.