Gold

Gold was the color of death. He was a vampire and Seishirou was merely a human. If that's so, then why is Seishirou's eye a bright gold like his?

Death

Subaru was afraid of death. He, himself, ages much slower than humans so dying does not scare him much. It's when he saw Seishirou on the brink of death that got him so panicked that he gave him his own blood. Turning into a vampire was like dying but Seishirou would live much longer. It was Subaru's selfishness to have Seishirou by him no matter what. He didn't want to lose him to anybody, not even to death.

Angel

When Seishirou first met Subaru, he knew right away that the vampire was filled with so much innocence. Even though Subaru was a vampire, he acted more like an angel. A beautiful angel sent by God himself.

Shadows

They were each other's shadows. Where one goes, the other will follow. One was nice, and the other was cruel. They cannot exist without the other.