Spirit Ashes are almost certainly relevant to ghostflame. Spirit ashes are probably the cinders of the ghostflame-burned bodies referred to in the deathbird lore, which cinders/ashes are said to cause vengeful spirits to arise (i.e. exactly what Spirit Ashes do). Just not sure if that's best put in the main body when it doesn't appear in any in-game item, or under trivia.
Hi, That's definitely a possibility. I wouldn't add it to the main body, but the link between ashes and spirits could work as a note.