Shinra was originally a part of the Tenkaku, a rebellion force which fought against the Horai in order to save the people who were forced to live under their rule. Shinra was a pilot that was sent out into combat, using fighters called Hitekkais. However, due to the Horai nation's overall strength, the Tenkaku was systematically wiped out, except for Shinra.
Days after the Tenkaku was destroyed, he had begun work on a new Hitekkai from the remnants of other fallen ships and fighters—the Shirasagi (lit. White Heron). He had prepared himself to keep fighting despite the rebellion failing, but he didn't expect himself to survive his attempt. For him, during the night as he slept inside his completed makeshift ship, he felt uneasy about his actions, thinking he was rushing to his own death.
The next day, he let himself be seen on the defense radars of the Horai, and allowed himself to be attacked by their own Hitekkai fighters. Displaying his skills as a pilot, he destroyed countless ships with what was supposed to be the inferior Shirasagi. However, the Butsutekkai unit Eboshidori (lit. Turaco) entered into the battle, piloted by the Horai General, Asami Kagehisa. With the two taunting each other, they fought, despite how outclassed the Shirasagi was compared to the enemy unit. However, still displaying that skill from earlier, Shinra was able to keep up until a series of homing missiles was launched at him.
The Shirasagi was instantly crippled by the attack and began to descend down, leaving behind billowing clouds of black in its trail. Asami hoped to fight Shinra again, if he survived the crashing of ship. Without any further words, he left, while the Shirasagi was left to collide with the ground below.
The location of its crash site was in the mountain where a village of located, the Village of the Grosbeak. Its inhabitants, which mostly consisted of the elderly, pulled Shinra from the wreckage of his ship. For two months, they let him rest and recover from the crash. The village elder, Kazamori, after asking Shinra why he fought, led him to a hidden Hitekkai named the Ikaruga (lit. Grosbeak), a ship capable of switching between the two types of energy (or polarities) used by more Horai weaponry. Shinra will be the pilot of it, though because the Ikaruga isn't like normal Hitekkai, he'll need to be trained in its use first.
One day, an unnamed Butsutekkai unit had appeared overhead, Shinra heading out to destroy it with the Ikaruga. Using its ability to switch polarity and absorb the appropriate energy, he managed to stay as the winning participant in this dog fight. With the pilot of the Butsutekkai visibly unsure of how to take on the Ikaruga, Shinra let out one last attack, sending the unit falling in the direction of the village.
Fortunately for those in the village, the unit didn't crash land on top of them. Instead, it fell some distance away from the village, leading Shinra to check on the wreckage. Setting down next to the wreck, he noticed an unconscious female figure laying outside of the crash site (the pilot of the Butsutekkai). Shinra attempted to wake her up, but upon opening her eyes, she pushed him away from her. She begged for him to kill her, being unable to stand losing in such a fashion, but upon Shinra looking as though he wouldn't even dream of doing so, she decided to do it herself. Shinra stopped her, however, and took her to the village.
After weeks passed by, she had relaxed and was even listening to the birds chirping outside of Kazamori's home. Shinra talked with her, where she finally shared her name with him—Kagari. She asked why Shinra saved her (since she belonged to Horai), his only answer being that he didn't have the heart to let someone just die like that. She had heard discussions between Shinra and Kazamori about the concept of freedom, and asked if something if such a think really existed. Shinra wasn't sure, exactly, but felt that the freedom he wanted was out there, somewhere.
Out of nowhere, she wanted to head back to the wreckage of her Butsutekkai, promising that she wouldn't try to run away. Shinra reluctantly brought her there, where Kagari revealed a Hitekkai was hidden inside. The name of it being the Ginkei (lit. Silver Bird). She wanted it outfitted with the same kind of abilities as the Ikaruga, wanting to see that freedom everyone keeps talking about. After much deliberation, it was decided that that the Ginkei would be refitted with the same technology as the Ikaruga (though Kagari would need the training to handle it after its tuned to be like the Ikaruga).