Objectively speaking, for Akaza to become the apprentice of Touko was a complete accident for her.
Passing by that road was an accident, being attracted to a building that looked like an abandoned construction site was an accident, and miraculously avoiding most of the defensive barriers set up inside by Touko was also an accident.
But just as Aoko said, all these accidents together actually constituted an inevitable fact:
No matter what timeline it is, Akaza will always become Touko's apprentice.
However, if you were to ask Akaza herself, you'd probably get a slightly different answer, because between the two, it was Touko who first proposed to take on a student, and after a brief moment's thought, it was Akaza who immediately agreed.
The reason for this is not easily shared with outsiders, as it is one of Akaza's hidden secrets—though it was quickly discovered by Touko.
Akaza likes her brother, Mikiya Kokutou.
But it's not an ordinary kind of like; Akaza sees Mikiya as a man she wants to be with intimately. This has led her to take her strategy to win over Mikiya very seriously.
When Akaza was still in elementary school, she realized she was much more mature and outstanding than her peers, whether in looks, manner, or grades—she was far ahead of those around her. To some extent, this shaped her relatively cold personality.
Her feelings for Mikiya are long past the level of "wanting to be together." It's more like "wanting to have him all to herself" or "if possible, she'd like to hide him away from everyone else"—a level of possessiveness that absolutely cannot be revealed publicly.
Yet living together day and night, Akaza found herself in despair, unable to see any chance to transform their ordinary relationship. So, she came up with a brilliant plan: leave for a period, then suddenly return, and let Akaza see a whole new her.
Usually, for the daughter of a working-class family, this plan would be close to delusional. But Akaza was lucky: she had an uncle who was a famous painter. (Different from the original timeline, in this story Akaza has been attending the Reien Girls' Academy since elementary school.)
As her father's brother, her uncle was very wealthy, and since Akaza was an excellent student with outstanding looks, he was more than happy to sponsor such a niece to attend a prestigious girls' school—Reien Girls' Academy—allowing her plan to succeed.
Everything seemed so perfect. The highly capable Akaza also adapted very well to the life of an ojou-sama at the academy. But the unexpected still happened: three years ago, during a surprise visit home, she witnessed the last thing she wanted to see.
That ordinary, unremarkable Mikiya had found a girlfriend!
Akaza was speechless. To think that, besides herself, another girl would want to be with that idiot Mikiya! This cruel fact undoubtedly wounded Akaza's fragile heart.
She left her hometown dispirited and continued her studies at the prestigious academy. But as the saying goes, the heavens never completely shut the door on anyone: she heard by chance that the girl named Ryougi Shiki had been in a traffic accident and had fallen into a coma—Mikiya was single again.
Akaza certainly wouldn't let such a godsent opportunity slip by. Although it was said that Ryougi Shiki suddenly regained consciousness last year, she resolved to make her move before Mikiya and the newly awakened Shiki could rekindle their relationship—to win Mikiya over.
For this, Akaza wouldn't give up any opportunity, and becoming the apprentice of Touko was, in her mind, the best chance to defeat Ryougi Shiki and win Mikiya!
"Huh? So that's what you were thinking?" Aoko said in realization after hearing Akaza's plan. "Such impressive resolve—Touko's found herself a great student~"
"Thank you for your praise!" Akaza felt deeply honored to be complimented by the famous Miss Blue (even though she'd just heard of Aoko for the first time).
"By the way, did Touko ever tell you about your origin?" Aoko suddenly asked.
"Yes, Teacher Touko told me—my origin is 'Taboo'," Akaza replied frankly. "I also know that's the root cause of why I like Mikiya. But that doesn't matter, because I know my feelings for him are real!"
Seeing Akaza's powerful confidence and unwavering will, Aozaki Aoko couldn't help but show a mysterious smile.
"Hey, Akaza, I wonder if you've ever considered this," Aoko said slowly, "If you like Mikiya because you're attracted to the forbidden, then… if Mikiya and Ryougi Shiki got married, and you still pursued him behind her back, wouldn't that be even more forbidden?"
Akaza's body froze instantly, trembling slightly as if she'd finally glimpsed an unspeakable truth hidden in the abyss of the world.
Although Akaza understood that her teacher's sister was probably teasing her for amusement, she had to admit that Aoko's suggestion did hit the spot.
….
Aoko used a teleportation spell to visit the Kuonji estate, asked Habetrot to make her a Reien uniform, and then, together with Akaza, Touko, and Alice, disguised themselves as ordinary students and blended into the secluded Reien Girls' Academy.
"Where did you go to school in middle school, Miss Aoko?" Akaza asked as the group walked along a forest path.
"Not Reien, but I did attend a similar ojou-sama school," Aoko replied with a smile. "It was Reien's old rival, Asakami Girls' Academy."
"Really? I thought you would have graduated from Reien, like Teacher Touko and Alice-senpai," Akaza said in surprise.
"Back then Touko and I even got into a big fight over family inheritance. How could I possibly follow in her footsteps and attend the same school?" Aoko laughed.
"Is that so? I always thought you two got along well!" Akaza exclaimed.
"We do get along well now," Aoko said as she hugged Touko's arm, leaning her head on Touko's shoulder in a show of sisterly affection.
"Stop it! Let's finish the job quickly," Touko said, pushing Aoko away with a look of annoyance. "I have a lot of work to do. Not everyone has the time to play at being a high school student and goof around in school!"
From an outsider's perspective, this was just an ordinary, youthful, intimate interaction between high school girls—enough to make someone sigh, "Ah, what a beautiful world!"
But appearances often differ greatly from reality. The young, beautiful girls might well be world-destroying demon lords in disguise.