No.6 Discussion Board

I always thought the injection was probably one he got as a child. Like, after the 2-years-examination but before his first meeting with Nezumi? Young Shion already thinks that he's not someone to get in trouble just to help someone he barely knows; although he does make an exception for Nezumi. So I'd say the egg is already factoring in there.
And agreed - something eating through nearly your whole brain is definitely not good. I'm no ace in neurobiology either but I'm pretty sure those parts are all pretty important. I think that maybe it wasn't just the stress alone that saved Shion. @Meopat wondered why Shion got that blister on his neck and I think that maybe the egg didn't place itself in the right spot? Instead of planting itself into his brain it may have stayed in his neck and when it prepared to hatch due to the stress indication, the blister started to form. I mean, it's rare but it does happen that a parasite doesn't find the right spot in its host. Which usually results in lethal conditions but who knows maybe Shion was lucky xD

Oxygen radicals are one of the most dangerous radicals you could have. They're highly reactive and alter almost anything they can get to - proteins, DNA. Subsequently, cells die. Actually, our own immune system uses mechanisms that work like that against bacteria and parasites.
But no. No scarring or hair colour changes. At least not so fast. I mean, if the radicals altered the DNA to be unable to produce melanine but not enough to kill the cells, it would be possible for Shion to grow uncoloured hair. But that's highly unlikely, really ^^"