NOTE: I know that Gengo is Kazuya & Kazuha's grandfather in canon, but for the purposes of this story I made him their father instead.
Humanity is under attack.
Aliens from another dimension, dubbed 'Nova', were attacking the world. No one knew why they were doing it, only that it was very much a real threat. Conventional weaponry and tactics have proven to be ineffective against the Nova, which meant alternatives had to be explored. Backed up against the wall, humanity's leaders organized the Chevalier organization. An elite military organization tasked with combating and defeating the Nova. That's where he came in to the picture. Dr. Gengo Aoi. His expertise in genetics was unparalleled, and with the motivation to fight the aliens he was the perfect candidate for their intelligence and research division.
His work along with a few other brilliant minds created the Pandora and Limiter projects through genetics and stigmata manipulation, the means with which humanity could fight back against the alien aggressors. The success of the Pandora and Limiter projects gave humanity a fighting chance, and yet he knew it was not enough. To ensure the survival of the human race, he had to do more.
That is why you have to do it. To save humanity. He reminded himself that what he was about to do was necessary for the survival of mankind. Still, it left him uneasy that he was going to be using his own children in such a manner. His own flesh and blood. What would his wife say if she were still alive? He swiftly squashed the thought from his mind.
He did not want to think about that. Not in such a critical moment. He opened his eyes, having had them closed for the last few minutes as he battled internally with himself. It must be done. He eyed the two tiny bodies that were held in identical stasis chambers. They were immersed in a green liquid, floating unconsciously with numerous tubes and sensors attached to them.
Today was the culmination of the work he had done for the last three years on them.
Since their birth, he had started the experiment and much to his pleasure and surprise things progressed well. Very well. So well in fact that he not only extended the project, he upgraded it. Now he was at the last stage. There were two possible outcomes to this night, one of which was death.
I won't allow it, he thought as his body stiffened. It'll work. It has to...
He took a few deep breaths to calm himself. He needed to focus. Success would be guaranteed if he performed the final stage flawlessly.
Alone in his personal laboratory, he began the final stage of his project. It took him several hours. His body protested from the strain, particularly since he had to do everything himself without any assistants, but he ignored it. Mind prevailed over matter. When he finished, he fell to the ground in exhaustion. His breathing was ragged, his body shaking and drenched with sweat.
His tired eyes looked up at the two stasis chambers.
Everything had gone smoothly. There were no issues that popped up. No unexpected problems. It seemed almost as if it was meant to be. He sat on the ground for a while, his back resting against a computer terminal as he simply watched his children with relief. After a while, he struggled to get up. He swayed slightly, unbalanced, but managed to keep himself upright.
He walked around to the main computer and checked the results. His eyes scanning the multitude of numbers and data that the computer was displaying on the screen. Everything seemed to check out. All vital signs were stable. Stigma tissue had been completely accepted by their bodies - no compatibility issues whatsoever. The project had been a roaring success.
Still, he did not feel as triumphant as he thought he would be when he imagined this moment. All he really felt was a joyous relief that they had survived, and a strong sense of hope that humanity may yet be victorious in the end. Looking back at his children, he took comfort in knowing that they would live to have a future.
That made him think about the fact that what he had done to them meant they really only had one future. He had chosen that future for them, and he hoped that they would understand why he did it. He hoped that they would understand and believe in it. That they would embrace their future.
Their future as humanity's hope.
Author's notes: I really like this anime and hopefully I can do it justice - I have not read the manga.