Disclaimer: I don't own A Certain Magical Index or it's spinoffs, Kazuma Kamachi does.
[TKK]
Touma Kihara Kamijou
[TKK]
From behind the scenes, in Academy City, unethical experiments were largely performed by the men and women of the Kihara Family just for the sake of experimenting. Despite the great scientific successes spawned from their actions, the trauma and deaths incurred on their test subjects as well as those at the wrong place and time left the Kiharas with a bad reputation for those who knew of their existence. Nonetheless, for pragmatic reasons, the Kiharas, along with the rest of Academy City's Dark Side were largely left alone by the Board of Directors. In fact, the Board's illusive Chairman had called upon his allies in the Family to aid him in securing an important part of his plan by the name of Touma Kamijou.
It wasn't that hard in following the trail of bad luck in the form of a delinquent mob running after Touma to get to him. What was hard, was that his right-handed power which the Chairman, Aleister Crowley, called the Imagine Breaker negated Esper abilities as well as what he referred to as Magic. The young adolescent's argumental and idealistic attitude didn't help much either. However, the Kiharas were able to get him alone, and with some convincing that they weren't as immorally deranged as one would describe them to be, they made Touma an offer that would change his life.
[TKK]
Many years later, at the Multi Active Rescue Base Research Laboratory which was under the authority of Therestina Kihara Lifeline, the experimental laboratory had been placed in her charge for a particular study of the Accelerator ability involving herself, one of the older member of her family, and the senior Kihara's youngest protégé.
"All right, then, Touma, fire away." The super-intelligent golden retriever, Noukan Kihara, called out to his young student who, like him, was a member of the Kihara Family in conceptual terms than that of literal blood relation as a large fan was blowing wind at Touma's direction.
Touma conveyed a confidant grin before using his left hand to re-vector the wind to form an extremely high velocity wind. His Aerokinesis was off at a good start before it eventually dissipated into nothingness.
While it was true that Touma's Imagine Breaker kept him from becoming a full Esper or Magician, Crowley had a theory that since the Imagine Breaker existed only in his right hand, then it would be possible to implant either abilities by focusing into any other part of his body, and since he wouldn't be considered a full Esper or Magician, he would be able to interfere in both the Magic and Science Sides without greater repercussions. After much effort, they were able to give him the Accelerator power that was once only used by Academy City's strongest Esper, even though Touma used his variant without the good degree of calculation and overwhelming force that the aptly named Accelerator was known for. Upon the experiment's success, Touma decided to continue working with the Kiharas and Crowley, if for no other reason than to counterbalance the harmfulness of their actions. It wasn't an easy arrangement, but it he liked to believe that it kept the peace for a time.
"Well, it's still abundantly clear you lack the calculative strong point of the real Accelerator, your use of Vector Manipulation will still be useful in making him into a Level 6 when the time is right." The beautiful Therestina stated before showing a small smile. "Good work, Touma."
Touma bowed in appreciation. "It was my pleasure, Captain." He then turned to Noukan. "Anything else on the agenda today, Noukan Sensei?"
Noukan shook his head. "No need, young friend. We'll work again tomorrow. For now, enjoy the rest of your day."
Noukan then left the laboratory, leaving Touma alone with Therestina.
"Well, I'll be going now, Captain." Touma said after an awkward moment of silence. "Let me know when Commander Amata decides to play ball with you."
About to leave himself, he found a hand placed upon his shoulder and turned around to see Therestina looking at him with half lidded eyes.
"Come now, Touma." She said seductively. "Didn't I tell you that you're more than welcome to call me Therestina?"
Touma gulped nervously. "Just thought I'd show you some respect, that's all."
She giggled childishly. "I'm hardly the Queen of England, Touma, any more than I'm your school teacher. Which means I get to play around with you at some points, whether you like it or not."
Therestina then closed the distance by kissing him on the lips.
[TKK]
I hope you people don't mind the little theory I let out. It might be a bit convenient, but there are so few A Certain Magical Index stories on FFN and perhaps other sites, and none that I know off used this particular AU and pairing before. Looks like I'll be keeping busy with other fandoms after all. Hope this inspires you in your writing.