I always saw it as an abstraction of expanding your Overall mining operations, and to implement mechanically how an empire, over time, goes from having only a few elite soldiers/champions clad in iron armor, to having many troops clad in iron armor
On a similar vein of thought, having "specialty weapons" (like Katana +1, although in this case it would be Katana +3...) should cost significantly more Iron.
This could be tweaked by balanced, but lets say a regular Katana of 6 attack costs 5 iron, while a prized Katana +3 (9 attack) uses 10 iron, and a master work 12 attack Katana could require 20 iron.
To represent the extra time it takes to forge such weapons, as well as the more metal (although perhaps not *as much* more) required for the process of multiple refoldings.
A theoretical Hittori Hanzo Katana would require a special Quest-gained technology, have 24 attack, and would require 50 iron.
Now, the numbers could be tweaked ... even to the point of a 1:1 ratio if Swarm tactics prove more effective than giving an awesome super weapon to a leveled Champion (although I would hope this were not the case).
Additionally, perhaps training a soldier with such a specialized weapon would add extra turns to the "training time" although it would probably be better to store this extra time as a necessary material for item creation. Abstract perhaps, yet if you were forging a Hittori Hanzo blade for your Soveriegn, it would still take say 5 turns (or so) for the weapon to be created (as opposed to immediately).
Perhaps an additional requirement of the Hittori Hanzo blade (placeholder name for a buildable, mass producible, super weapon that is found via questing) could be that only one such blade could be under production at a single time (within a city). This could be facilitated by having the blade require a special building be present within the city. My preference would be that the building would be a national wonder ... meaning any given faction can only build one such building at any one time. Therefore, you can only build one Hanzo blade at any one time, and only in one city, and only after you build the special building. If its just blue-prints for a one-time legendary weapon, however, then it doesn't need any such restrictions because you would need to obtain a very rare material for creation.
Below lies the Heartblade
Personally I would like to see a Weapon (or armor) blueprint that has under required materials a Dragon's Heart. (Heartblade) ... then, for any given Heartblade (at the time of creation) you can make it more powerful by adding more gold and magic crystals (like a slider system for price/utility). Then, there would be several optional *specialty* materials (can only choose one specialty material) ... like a Sapphire Orb, Talisman of Souls, or Obsidian Mirror. Depending on the specialty material used, the Heartblade takes a different form with different special powers (in addition to the already potent Attack skills of the weapon).
For instance, the Heartblade without any specialty materials could have a high attack (17), with a 33% chance of a "heart strike" which automatically deals 5 damage regardless of attack role (except vs large creatures) and adds +10 to the attack role. The 5 damage would not stack with sucessive damage dealt by the attack role, so if the attack of 27 dealt 5 points of damage (after initial 5) then it wouldnt ... as in only 5 points of damage would be dealt. However if the attack of 27 dealt 10 points of damage, then 5 additional points of damage would be dealt.
Vorpal Heartblade (Talisman of Souls) would give +1 death damage for each strike, as well as slowly draining the morale of nearby opponents.
Pristine Heartblade (Obsidian Mirror) would have a 25% chance of reflecting damage that would of been recieved, and instead inflicting it on the attacker. This works for magical attacks too. Pristine Heartblade also grants the wearer immunity to fear, poison, and disease.
Glimmering Heartblade (Sapphire Orb) doubles the attack speed of the wielder. Extra speed (over 10) is translated into increased attack. 20% chance to evade physical attacks, 10% resistance to magical attacks. Immunity to fatigue and time spells, as well as a 33% evasion chance for single target magical attacks.
Eaglet Heartblade (Silver Goblet) doubles movement speed and allows flight. Immunity to Air magic, and 75% resistance to ranged physical attacks.
Carnal Heartblade (Female Champion/Princess"death"- or - Ruby of Desire) +2 attack speed, +4 strength, 50% of damage dealt is absorbed back into the wielder (for a temporary max of 150% total HP, meaning a 60 HP champion could hold 90 HP during a battle, after absorbing 30 HP). 20% resistance to physical damage, 50% resistance to fire damage. 20% weakness to ice damage.
Adamantine Heartblade (Adamantium Ore (rare) + Crystal of Resonance (moderate/uncommon)) wielder is 80% resistant to physical damage, and 50% resistant to magical damage
Golden Heartblade (Heart of Midas) each kill turns into gold (+50 gold for a human, +200 gold for medium sized monster, +500 gold for large monster, +1000 or so gold for gigantic monster kill). In addition, 80% chance to evade any lethal attack ... if Golden Heartblade user has 4 HP, and an attack deals 5 damage, the user has an 80% chance to completely dodge the attack.
Silver Heartblade (Tooth of the Silverine)- ignore 50% of the defender's defense rating. (alternatively, ignore non-magical equipment based defense)
Mystic Heartblade (Statue of Jade)- ignore status affecting magical attacks, ignore opponents magical defenses (vs damage or status affects), 50% resistance to magical damage
Static Heartblade (Jewel of Zeus)- +5 electric damage with each attack, 85% resistant to electrical damage
All Heartblades (or other unique/extremely rare weapons for that matter) drop onto the battlefield after the wielder has been slain. Such weapons appear as loot for the victor of the battle.