What Noble Phantasm/Mystic Code/other magical artifact could Shirou Emiya been implanted with after the fire to save his life, other than Avalon? How would it affect him?
Fate/Zero Drama CD 3
You can find all seven here, three are subbed
It could be just speculation. I think Nasu said he was sort of reborn at that moment and it shifted his origin/affinity. Naturally a scabbard goes with a sword and maybe his soul was trying to compensate.
One of the crystals from ORT
It would turn Fate/Stay Night into a tentacle rape doujin