Iron and Leaves
Magically summoned spirit assassins. They travel in wind and are invisible until they attack, at which time they form into a visible wind cyclone and only their attacking weapon (traditionally a sword) becomes visible as it extends out of the cyclone to attack. After each attack, the cyclone vanishes and the creature is invisible again until its next attack.
Spells, miracles, and enchantments that grant supernatural sight will reveal the construct, effectively negating the invisibility. Folk magic cantrips reveal only construct and not the spirit within, though more powerful theism miracles or sorcery spells might.
They are constructed out of weapons tied together into a stick figure of sorts, then a demon or spirit is summoned and bound into the construct. They are usually used as assassins and the names of their target or targets must be written down and attached into the construct during the creation.
It is not a commonly known spell and in most parts of the empire it is strictly illegal due to its intended use of assassination.
In [[Book 1, Chapter 1: A Cold Beginning… | chapter 1]], a sword wind was sent to assassinate all four heroes. In [[Book 1, Chapter 5: Assassins in Old Town | chapter 5]], they learn that it was created by Master Rankins.