kresnik wrote:
Although magic items generally can't have runes, this does pose a good question for a Kio Sword, which requires attunement and with the magical family heirloom rule can gain an uncommon rune at 7th level. If one chooses a rune which requires attunement(such as a spell rune), would the sword and its runes still only be one attunement slot?
I hunted this down awhile back:
Forged In Magic: Reforged p178, Rune Quality and Slots wrote:
Very rare and legendary runes require the wielder to be attuned to the item bearing the rune in order to gain their full potential... (emphasis mine)
So, your fancy heirloom kio sword costs you one slot, not one per rune. Likewise, it seems likely that Eric's original question about the oddball magic items that accept runes (ex. Ring of Earth's Mettle) should fall under the same rule: one item, one attunement slot, unless item text overrides.
Nobody official here.