The Storm Witches of the Under the Sea sidestory? It has long been speculation that Xuan Shi's ancestry runs also through the Sea Folk in addition to the Xuan bloodline, and this tidbit seems to add more evidence in support of that theory. (Can't be from the wreck mentioned in the sidestory: that should have been in the western region of the Sea Folk's territory. But where else could a Xuan captain obtain a Sea Folk talisman?)It was an odd little charm carved from a light wood which Ling Qi didn't recognize. Under her spiritual senses it seemed drenched in the qi of the sea. Wrapped around the wooden idol was a lock of dark hair, bound by twine. "A keepsake of mine father, but the carvings seemed familiar to some of the descriptions in Elder's work."
"Sea folk work," grunted the sword. "Northeastern region. Done by the Storm folk, their surface colonists going by the material
Unless it's a war trophy -- seems kinda odd for Xuan Shi to value it so, though -- this charm looks like a token from a Storm Witch to Xuan Shi's father, an especially intimate one, too. The lock of hair seems to probably be from the Storm Witch, since the Xuan grow little hair and the sole Storm Witch we've seen had overgrown dark hair as a mark of their separation from the undersea folk.
(Also, note the word 'colonist.' The explanation for the Storm Witches given in the sidestory was that the Storm Witches are exiles; that the sword thought they were outposts of the Sea Folk is another expression of the Empire's self-centered perspective.)