The Coalheart: A device of some prominence in the history of the European Empire, believed to be the first instance of a device base for an Artificial Changeling. Allows immortality so long as it contains burning coal, although it may be possible to substitute wood instead. Over time, the blood of it’s user turns black as it dumps smoke into their veins, this is faster if they take advantage of the ability to avoid eating or breathing normally.
Natan-Natan, the Sword of Exile: Retrieved from the Castle of Loss in the First Timeline by Fourth England only recently, so its history is mostly unknown. Capable of opening portals to banish or cut targets, and while said portals are connected to a pocket timeline unique to the sword by default, the target can be changed with training. It carries a strong impetus to never return to the place where one gained the sword until one gives it up, although this is not entirely compulsory. Can also be used to make access to an area difficult, although this is a more advanced function.
The Seal of the Amethyst Emperor: Used to authenticate the lords of noble houses, as well as every new set of Samurai armor during the reign of the Wandering Empire, effectively controlling the military and symbolic strength of the various factions. It is therefore of incredible cultural and strategic value, and whoever it recognizes as its master was the rightful leader. It cannot easily be stolen, as it will burn those who take it from a rightful master without leave, and can be summoned at will by its rightful master, to which it is spiritually linked, and similar measures are in place to prevent its destruction. It will only acknowledge a ruler who fits certain criteria, determined both at the time of its creation and by the previous emperor at the time he last held it. In modern times, its use is almost purely ceremonial, but if the need seems dire, it may once again grant its blessings to worthy servants...
The Thousand Blades of Battle: A more mythical Piece, straddling the line of full Eidolon, The Thousand Blades of Battle are a collection of weapons that appear to worthy wielders in moments of need, generally with the restriction that they be carrying a blade of their own to give it in trade. It contains at least a thousand Archetype Pieces of varying power, and is suspected to absorb any sufficiently unclaimed blade that has been used extensively in true, if not mortal, combat.