After Flare joined Fairy Tail, Ben and Mira train her magic. They also teach her many things about the world, especially common sense. She doesn't know much about this world, so they need to teach her like they teach a child.

But after a few days, they find out that Flare is quite mischievous. She likes to tease others using her rather scary expression and hair. The one that she likes to tease the most is Lucy because her reaction is the best.

Other than training Flare, Ben is also doing research to improve his training. He had finished scanning all the books in the Magic Library. So now he wanted to learn about magic from other nations in Ishgar.

Fortunately, with his position as a Wizard Saint, it is quite easy to get a lot of magic books. He asked the Magic Council and other Wizard Saints for help. It needs a lot of money, something he had a lot of.

The books will take a long time to gather, so he will take jobs while waiting. Normal S-Class jobs are too easy for him, so he needed to take a Decade Quest. He can't leave right away though because he needs to make sure Flare can be left alone in the guild.

Ben finally dared to leave Flare on her own after a month. Then he took a Decade Quest with Mira because they always wanted to do it. But in the past, they couldn't do it because they needed to save the Tenrou Team first.

The quest that they take is the exploration of a cave in the nation of Deserto. A lot of mages have taken this quest but no one succeeded. Only a few could return alive and they all said that the cave is a giant maze full of demons from the Book of Zeref.

There isn't enough information about the cave, but that wasn't a problem for Ben. As a Devil Slayer, he had a lot of confidence that he could defeat those demons. Mira's power is also effective against demons and she can take over a demon if they find a strong one.

Ben and Mira go to Deserto in Light Runner as usual. They need to cross some nations, but it wasn't a problem with Light Runner's speed. It still took 5 days even though Ben drove really fast, but it's still faster than other modes of transportation.

The cave is located in the middle of a desert as Deserto's land is mostly desert. It's entrance is in a big red rocky mountain. Ben can feel the ominous aura and magic power even when the cave entrance wasn't in sight.

"It's no wonder so many mages failed this quest. From the magic power alone, I can predict that there are hundreds or even thousands of them." Ben said.

"Are they strong?" Mira asked.

"Not sure, but I don't think so. I think they're just low-level Etherious that can't speak human language, just a bunch of mindless creatures. That number is still a massive threat to most S-Class mages. Even Laxus and his team will have a hard time here and might be annihilated." Ben answered.

Mira had expected that level of danger for a Decade Quest, but it's still shocking to hear that even the Thunder Legion would be annihilated here. Those guys are the strongest team after Ben's team.

"So, what's the plan?" Mira asked.

Ben smirked.

"Let's just fight them until we get dead tired." He said.

Mira had a stunned expression before sighing. "Do you really need to do this?"

"Of course. I haven't had a thrilling battle for so long. You know it too, that tough battles are the best way to grow stronger. But that's the biggest problem for me right now. There aren't too many opponents that can force me to use my full power so it's difficult to use this method. I need to grow stronger fast before Acnologia makes another appearance. This is the only method that I can think of before I can improve my training." Ben said.

Mira just sighed. "Make sure you don't die."

Ben nods and Mira doesn't say anything else. She knows that she can't stop Ben and there's no reason to stop him. He has set his goal and he will do anything to reach that goal. Also, he's not reckless, he has plans with a high chance of success.

The cave entrance finally came into view and there is no demon at all. All of the demons seem to be inside the cave. Ben thought that it was very strange for Etherious to just stay silent inside a cave for a long time.

"This is a Decade Quest, so I assume that the demons have lived in this cave for almost 10 years. But there aren't any records of them attacking even the nearest town." Ben said.

"It's definitely strange. Aren't Etherious usually thirsty for blood? It's quite unbelievable that all of them will stay in one place for a long time." Mira added.

"Unless someone or something is commanding them. The only one I can think of are higher-level Etherious. There might be a very high-level one inside there. An Etherious with a higher level than anyone that we've encountered." Ben noted.

Ben and Mira prepare themselves before they enter the cave. It's very dark inside and normal light magic can't even illuminate it completely. So Ben used his Sun Dragon Slayer's Light Magic that has the brightest light to make some big and bright light balls.

"The Sun God Slayer's Light Magic is useless for this kind of thing. It's powerful, but it's black and dark. What's the point of dark light?" Ben complained.

"Well, everything has it's good and bad side, right? In exchange for power, God Slayer Magic's elements lose their reliability." Mira pointed out before changing into her Satan Soul form.

Ben sends his light balls ahead of them while a light ball was kept on top of them. Now they can see the cave interior and it really can't be called a cave. The correct name for this place is a dungeon or labyrinth.

The dungeon corridor is square and it's very wide even though the entrance is quite small. There are many engravings on the floor, walls and ceiling. Pictures, symbols and letters are engraved all over the surface.

Ben was interested in all those engravings, so he decided to inspect them first before going deeper. There might be secrets hidden here. Who knows? Maybe he'll find a Lost Magic if he's lucky.

Mira sighed when Ben told her about his intention, but she can't do anything about it. So she cancels her transformation a moment after she activated it. She took a sofa out of her storage space and a tea set as well so she can wait until Ben finished his inspection comfortably.

Strangely, no Etherious approached them even though they didn't hide their presence. The two realized that there were a lot of Etherious that were watching them from deep inside the dungeon. None of them attacked though and Ben found out why a half hour later.

"Oh damn, so this is why the Etherious didn't attack any town. Correction it's not that they didn't, they can't." Ben said with a smirk.

"What do you mean?" Mira asked.

"There are several layers of enchantments here and they all have one purpose, preventing the demons from leaving this cave. All these enchantments are high-level ones too, so they didn't break even after a long time. These enchantments are at least 200 years old." Ben explained.

"But isn't this just a Decade Quest?" Mira asked.

"It doesn't matter, the quest means that the cave was discovered less than 100 years ago. As you know, Decade Quests aren't actually quests than haven't been completed in 10 years, but they haven't been finished for at least 10 years. The only quest above it is the 100 Year Quest."

"So, unfinished quests within 10-99 years are called Decade Quests. The case with this cave is that it was discovered by a high level enchanter in the distant past. That enchanter set up these layers of enchantment. It was probably because they couldn't kill all the Etherious, so they sealed the cave off. The country had just found this cave decades ago and handed out this quest that hadn't been completed in years." Ben informed her.

"...Oh, okay." Mira replied, confused.

Ben grinned.

"Anyway, I've finished my inspection and got some good enchantment data. Now, let's start subduing them." He said.