Long ago, Shiller seriously considered how to enable communication between two worlds. This was not to suggest a fusion of the two, as such an amalgamation could lead to many unforeseen circumstances.
However, appropriate interaction was necessary due to the stark differences between the two worlds, which naturally meant areas could complement each other. The last time Primary Universe Batman's soul accidentally entered Stark's body, the collision of their wisdom produced many positive effects, but that was merely an incidental event.
Shiller had been wanting to find a stable channel for characters from both worlds to interact, but sadly, as a human, he did not have the detached perspective of a god. What was clear to gods appeared mysterious to humans.
Yet Shiller did not set out to understand gods as a mere mortal; he decided to direct the gods himself.
Even god-like beings need specific counterparts. Shiller attempted to explore Eternity a few times previously, but he did not seem to grasp the affairs beyond the vast world, suggesting that he might just operate on commands without understanding the deep-seated secrets of the vast void.
Shiller was aware that OAA probably knew everything, but directing OAA was too troublesome and came at a substantial cost, so Shiller settled for second best, aiming at Oblivion, who was one of the five gods but the most mysterious of them all.
As it turned out, he was right. Oblivion was on the same level as Eternity but due to its special traits, it indeed understood more about the nothingness beyond the vast world.
Oblivion didn't explain to Shiller the structure of the universe beyond the vast world, but when Shiller proposed his hope to establish a channel between the two vast worlds, Oblivion did not immediately refuse but began to think. This suggested that Oblivion might indeed have the ability to create a passage in the void.
However, Oblivion raised a crucial doubt about Shiller's plan to create a hole: Shiller was an outsider who could freely appear in these two worlds, but how would he resolve the copyright issue if he transferred a character from this universe to another?
This was a question Shiller had contemplated, and the conclusion he arrived at was that it should be fine as long as he didn't make a noise about it.
This answer might seem ridiculous, but it was the result of rigorous deduction. After Primary Universe Batman arrived in this universe, there wasn't any universe-wide alert, no signals indicating to Universe administrators about the intrusion of a character from another universe.
Only later, when Shiller set up a situation forcing Batman to utter his most iconic phrase, did Eternity belatedly realise a big shot had arrived. This suggests that in cases where it isn't a problem for well-known characters to cross-visit, it really isn't a problem.
It makes sense upon reflection. Both DC and Marvel comics have extensive fandoms. Many, unauthorised, fan works exist. Even copyright hound Disney can't possibly go after each one, as there's no point.
Firstly, fan writers make negligible income; it's not worth mentioning. Secondly, fan works can significantly expand the original works' influence. If all incentives were removed, and copyright rules strictly enforced, neither of these comic companies would have as wide an influence, despite powerful publicity efforts.
From the standpoint of a transmigrator, if both vast worlds were to strictly enforce copyright, they could program an immediate alert into the fundamental rules of the universes, indicating to Universe administrators to remove any detected external life forms. However, after several tests, no such signals were observed. This proves there's no problem with inter-universe travel, as long as it doesn't cause great chaos.
However, just to be safe, Shiller decided that the first planned attempt at transmigration should be limited to an independent space with connections to the native universe but also sufficiently distant. This setup would be less likely to get noticed and easier to handle should problems arise.
Shiller had conceived this idea well in advance, hence when Bruce wanted to establish a magical school concealed beneath the Gotham River in the Magic Realm, he suggested expanding the plan to construct an inner world of Gotham directly. This perfectly complies with the conditions of having connections to the native universe but a certain distance for easier problem-solving in case of contingencies.
All was set, save for a catalyst. For Primary Universe Batman's contribution to Marvel, Shiller initially intended to bring Stark to the Prime Universe to assist the Primary Universe Batman. But, Stephen Strange took his own life, and keeping in line with his ever forgiving temperament, Shiller kicked him into the hole that Oblivion created.
There was a silver lining though – during the construction of the inner world, the remaining Magic Realm residents gave considerable help, contributing significantly. Now that the construction of the inner world was almost done, it was time for Batman to reciprocate by constructing the Magic Academy.
But after the vampire invasion and the Demon King cutting off supply, too few people were left in the Magic Realm, and even fewer were capable of being teachers. Even if they pushed people like Zatanna and John Constantine who weren't exactly suited to be teachers to step up, there would still be a lot of vacant professor positions.
But Strange had accumulated rich teaching experience in the Dreamland School and could suitably fill in as a professor in the Magic Academy. More importantly, his ethical standards were consistent with Gotham's requirements, ensuring he wouldn't be shocked by any startling remarks made by students.
This was critically important. Given Shiller's knowledge of Gotham University students, the papers submitted by many of them could literally be categorised as psychological pollution. It was universally acknowledged that these submissions were so extreme that even the cruelest and wickedest Black Magicians from the Magic Realm would express, in astonishment, "You're too extreme". These aren't meant for teachers with strong moral values.
Strange was an archetypal human supremacist, with a pretty narrow definition of the human race. You must consider yourself human first and not have betrayed the human race in your actions. Anyone else was considered an outcast, and he wouldn't flinch at their deaths. This alignment was consistent with the tonality of Gotham.
When Strange snapped out of his initial daze, he looked rather confused at the two people standing before him. Shiller explained the current situation to him in the simplest terms. In summary – work or die.
Strange looked at Shiller with a complicated gaze and said, "So, you've set up a magical school in another world, and because you lacked professors, you brought me here. Now I must teach and supervise students here, otherwise, I can't leave?"
Shiller nodded and said, "In a moment, we'll first go up to meet our colleagues, then visit and familiarize ourselves with the school. Once everything is arranged, we'll start the first round of admissions."
"Starting the first round of admissions?" Strange raised his tone somewhat surprised, "So, until now, this school doesn't have any students?"
"Many things await restoration, Sir," Bruce said, "Are we going up now?"
"He is..." Strange looked at Shiller and asked.
"My student." Shiller answered briefly. Then he turned and walked towards the door. Strange and Bruce followed him.
After going upstairs from the basement door, Strange found himself inside a castle. It looked somewhat like a Gothic castle, but it wasn't old or gloomy. Instead, it seemed like it was just built, with a touch of dark style and grandeur.
At the first junction, Bruce turned in a different direction, Shiller said nothing and continued to lead Strange upstairs.
After climbing a slightly complex spiraling staircase, they arrived on the third floor. The floor was entirely covered with dark red carpets, and the doors had intricate decorative patterns, looking very vintage. Combined with magical candlesticks hanging on both sides of the corridor, it was quite breathtakingly fantastical.
"It looks like you've recreated the magical school from your Tower of Thought," Strange said looking at the decoration of the corridor, "But it's a little different."
"I've omitted some of the parts with no practical value," Shiller replied, opening the office door. "The magic in this world isn't as beautiful. It's better if students don't have any illusions about it."
Upon entering, the room suddenly brightened. The deep red curtains hung next to the large wooden French windows, appearing intricate and lavish. The smooth walnut floor reflected the sunlight pouring in. Professors dressed in wizard robes were congregated in small groups, finalizing the notes for recruitment. Constantine, rare in formal magician attire, with Baroque-style shirt and trousers, was discussing the curriculum with Master Andrew.
Hearing footsteps at the door, he looked up to see Shiller and Strange following him and quickly approached them.
"You're back so soon. This must be the external professor? Hello, I'm John Constantine."
Strange stepped forward and shook hands with Constantine. Constantine looked surprised at his own hand. Shiller interrupted him before he said something silly: "He comes from a world identical to ours, but there are no Gotham and Metropolis, the two cities are combined into New York."
"Let me introduce you. This is Stephen Strange. In his universe, people call him 'Supreme Magician'."
Instantly, all eyes in the room focused on strange. He calmly nodded in response to everyone's gaze and said, "It's not humility, but I'm not the strongest Supreme Magician. The one called the strongest Supreme Magician of all time is my teacher, the Master Ancient One."
"Presumably, he must've been a virtuous and talented Grand Mage." Constantine flattered, Strange nodded at him, "Hello, Master Constantine, are you also a professor of this school?"
When it came to this, Constantine forced a smile, nodded and said, "Yes, I'm a professor now, even the professor of the most important core courses."
"So what course do you teach?"
"Well..." Constantine hesitated as if finding it embarrassing. But looking at the increasingly curious eyes of Strange, he had to say, "Mainly to introduce the students to the Demon King and angels and teach them how to deal with these powerful creatures."
"That's to teach them how to fool the Demon God."
Shiller summarized expressionlessly, Constantine looked at him, annoyed, "We agreed not to mention that!"
Strange's eyes brightened instantly.