Rachel never bites Ragna in her short story though. I think--think, don't quote me on this--she draws a magic circle around him, it glows blue, sometime later Ragna....sort of wakes up, but not really, only his right (now red) eye open. He then drags himself to where the Black Beast's body was sealed, and is engulfed in darkness. Let me go flip through the past pages to find the summary.
But....I'm not sure anymore. The whole vampirism issue is, iirc, never talked about aside from Rachel's CT arcade ending, and that's only "oh yeah once I bit a boy with jade eyes. Felt good, man."
Both of his eyes are red? They look green to me. His right eye appears to glow red during Black Onslaught (or at least the part where Ragna's covered in shadow), though.
And y'know, we've never seen Rachel in direct sunlight. She might sparkle after all!
....
I'll get my coat.
(And just as a question, maybe we should move this conversation to the BBCS speculation thread? It makes it a little difficult to find actual info buried in this thread.)