Suggested listening: Samidare (Naruto Shippuden OST 2 Track 28)
Some people in this world filled with darkness are born with a special ability of Sight and Light. Sight allows them to see the darkness, and Light allows them to take that darkness into themselves, giving Light to the others until they fall like a comet, light consumed by the overwhelming darkness. Few, nay, close to none, are born with only one of them, because it is extremely dangerous. If you knew not the darkness you took in, then you could die easily. But such was the case of Kagamine Rin and Kagamine Len.
They were twins; Rin was born with Light, and Len with Sight. Though Len could not control his ability of Sight, Light was a conscious ability: Rin could control whether she wanted to use it. However, she did not know of it.
Len saw it. He could see the pure, golden Light his twin sister had. She shone like the Sun in his Sight. So did another man.
Kaito was another of those special people, took them in when he saw the two orphans. He had the ability to change whatever darkness he took in into Light, and he made sure to protect Rin from awakening her ability. He had once seen another child who had Light but not Sight, and took too much darkness. She died, despite Kaito's best efforts.
But even with his ability, he could not turn his own darkness into Light. As Rin and Len sat by his dying body, he reached to brush Rin's cheek. Rin caught his hand, and much to his dismay, he saw the darkness flowing over to her. She could not see it, and neither did Len, whose eyes were turned down, unwilling to reveal his tears. He tugged back on the darkness, but it did not come back. All he could do was stem the flow.
Rin gasped slightly as the darkness entered her, but she did not seem to mind their presence. Some sort of instinct showed her that Kaito seemed to be more at ease, and she smiled sadly, tears slipping from her eyes as Kaito died. Len looked up, mouth pressed in a thin line from the strain of suppressing sobs, and caught a glimpse of darkness against Rin's skin. He blamed it on the lighting, but as he watched, the black grew and covered her arms with a dark, sinister pattern. As if in a dream, he saw a black bird turn white, and flap away in search of freedom. A worried frown formed on his mouth, but he turned it to a tentative, if fake, smile when Rin turned to him.
Eyes widened in shock and terror when he saw crowds and crowds of black birds appear on the horizon, moving quickly and surely towards Rin. They crowded around her, trying to grasp her golden light with their dark limbs. Smiling softly, she crouched and reached out. Len started forward, but his way was blocked by the black birds. With an angry snarl, he ripped his knife from its sheath and started slashing away, barely aware of the darkness creeping onto himself. Just as he reached Rin, he saw her fall, Light spent.
The birds had brought her into the sky, and he followed them as he plummeted after Rin, desperate to catch her before she hit the ground. The white birds were trying to keep her up, so Len managed to catch up with her and hold her in his arms as they fell, together.
He would not allow it to happen, even if he had to let himself be consumed by the darkness. Blood red eyes opened as pure black wings spread. Together with a crowd of now-black birds, for they had eaten Rin's dark taint, he bore Rin into the sunlight. Darkness gone, she once more shone gold in his Sight.
You are Soleil, he thought as his resolve faltered and the darkness took him. Wings melted away, and he fell with his Sun.