My physics masters couldn't possibly be grand mages.

Xia closed the book and remained silent for a long time.

Einstein did not speak.

After a brief silence, Einstein sighed softly, "Similar large-scale persecutions of women occurred in Europe during the Black Death. Elderly, impoverished widows, living alone, are usually the most vulnerable and marginalized group in society, making them ideal targets. History really does repeat itself in striking ways."

“It’s still different,” Tesla said. “Our world didn’t have magicians, but this world really does.”

Einstein understood what he meant: "You mean... there's a problem?"

"At least... it's definitely not as simple as it seems on the surface," Tesla said in a low voice. "How did a group of women who know nothing sign a contract with those things?"

Einstein seemed lost in thought.

Tesla didn't continue the conversation, but instead turned and walked toward the bookshelves.

When he returned, he was holding a book.

Contracts and Bloodlines and the Encyclopedia of Magical Creatures

"This is a book I read a few days ago," Tesla said. "Humans have the lowest magical power of all magical beings, but as compensation, the gods bestowed upon us something that other magical beings lack—'intelligence.'"

"To compensate for this deficiency, people have devised many methods, such as hybridizing with magical creatures to produce offspring with greater magical power. For example... making contracts with magical creatures and sharing their magical power."

"So Cindy must have made a contract with what's behind that door?"

Einstein opened the "Encyclopedia of Magical Creatures" and turned to the last page, where Char saw the title.

【demon】.

Char opened his eyes. "So that door leads to...."

"Where's your diary?"

Char took the miner's diary from his storage space and handed it to Einstein.

Einstein flipped through his diary, stopped at a certain page, and pointed to a passage.

[April 1st. Old Hank went mad. He cried and said that something down there was talking to him, saying that his whole family was down there.]

His wife died three years ago, and he also lost his child.

"The only places in this world where people die, besides Heaven..." Einstein gazed at Char, "are Hell..."

"What did his whole family do to deserve this?" Xia Ya complained.

"Or perhaps, there is no heaven in this world," Einstein said from the side. "If there were, how could witches be allowed to exist?"

Tesla gave a soft hum.

He didn't comment on Einstein's statement, but pointed to "Contracts and Bloodlines" and said, "This book actually contains examples of making contracts with demons. In fact, magicians don't have any aversion to making contracts with demons."

However, making a deal with a demon is very dangerous. If you can't control the demon, you'll be devoured by it. Therefore, often those who make contracts with magicians are demons of low power, used to increase their magical energy.

"To be categorized as a 'witch' on her own, the one she contracts with must not be an ordinary demon," Xia said, stroking his chin.

Einstein got up, found "The Devil's Guide" on the bookshelf, and said, "Now that we've determined it's a demon, it's actually easy to find. Tunnels are full of ghouls, which is a classic feature."

Xia also realized something, "When that woman was preparing to capture Sylvia, it seemed like she intended to suck her blood."

"Vampires, huh..." Tesla frowned.

"There aren't many demons associated with vampires, especially not the greater demons," Einstein silently flipped through the thick illustrated guide. "This world obviously doesn't have vampire figures like Dracula, because that's from late 19th-century novels. But..."

Einstein flipped to the last few pages of the illustrations and placed them among them.

Xia peeked over and saw a name on each of the two pages, one on the left and one on the right.

[Cain] [Lilith].

"Is this really another world?"

Looking at those two names, Tesla finally couldn't help but frown.

"Why are the written languages ​​the same, the religions the same, and even some of the legends the same?"

"This world actually fits the definition of 'parallel universe' better," Char said. "It's just that the concept of parallel universes didn't exist in your time, so I used 'another world' to explain it."

Seeing the puzzled looks on Tesla's and Einstein's faces, Xia scratched his head.

"Let me put it this way." He stacked the three sheets of paper in the illustrated book in front of him together.

"For example, if you leave home this morning, going left or going right are two different choices. In the theory of parallel universes, both choices actually happen. In one world, you go left, and in another world, you go right."

He unfolded the three sheets of paper again and dotted the left and right sides respectively.

"The world that goes to the left and the world that goes to the right were the same at the beginning, but they diverged from the moment you took that step. They became two parallel worlds."

"Every choice creates a new branch. And under that branch, there are more branches, like a tree that branches out from the same trunk into countless twigs."

He looked at Tesla and Einstein and shrugged.

"This is a parallel universe. It wasn't created by anyone, but is the sum of all possibilities. The world we live in is just a branch of this tree."

Einstein remained silent, staring at Char for two seconds without saying anything.

"Parallel universes..." Tesla repeated, then looked at Einstein and teased, "Didn't you say before that God doesn't play dice?"

Einstein firmly believed that the universe follows a unified law. The core of the saying "God does not play dice" is that he does not accept any form of "randomness" or "multiple branches".

"If every choice splits into a new world, then God isn't just rolling dice, he's running a casino," Tesla laughed.

"Then let him drive," Einstein said, glancing at Tesla as if discussing something trivial. "I'm not going anyway."

Tesla's lips twitched slightly, but he didn't say anything more. He just checked the time, took out a sandwich from the paper bag, and handed it to Char, then to Einstein.

Finally, I took one and took a bite.

"Shall we go check out the restricted section now?" Tesla asked, wiping his fingers with a tissue after finishing his sandwich.

Xia remembered what Monra had mentioned last night about the third floor of the forbidden book section, which was one of the purposes of their trip.

"Let's go," Einstein said, rising to his feet. "Perhaps we'll find more detailed information about the witch."

They went up the spiral staircase at the deepest part of the East Wing.

At the end of the stairs was a dark gray iron door with no handle or keyhole; I didn't know how to open it.

As Einstein approached, something seemed to be triggered, and the iron gate silently slid open to both sides.

Behind the door is the first floor of the restricted book area, which is similar to the East Zone, except that the bookshelves are darker and heavier, and the corridor is narrower and more cramped.

It seems that few people come here; the air is filled with the musty yet still fragrant scent of old books.

They didn't stay there for long, but soon found the so-called third floor, which was a rather inconspicuous oak door.

If this weren't the only place that required going up the stairs, thus fitting the definition of "third floor," they wouldn't have thought there was anything special about it.

Einstein walked in front and pushed open the door—