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The canon:
Percival’s sister, known as the Grail Heroine, makes Galahad a sword belt out of her hair, which was cut off when she became a nun and which she had previously been carrying around in a box because of a prophecy. To the best of my recollection, there is never any mention of him taking it off.
The headcanon:
Galahad never stops wearing the hair belt. People notice it but are too weirded out or intimidated to enquire about it, with the possible exception of random old ladies like Dame Clarys. Her reaction to his explanation (something along the lines of, “This was given to me by a most noble lady…no, we are both aroace; she is a nun…was a nun; she’s dead now… I really needed a belt, and she had this box of hair… Why? There was a prophecy…) would be, “That’s nice, dear”, because she too is an icon.