Silverbloods are those whose blood gleam like polished silver when alive and are a dull grey when dead, an image of them bleeding being much like the spilling of mercury.
They have the ability to willfully control their blood as if by telekinetic influence for as long as it or a mass of it remains in contact with them, the metallic fluid being capable of being forced out through their skin if they don't wish to cut themselves, and can solidify their blood into silvery solid objects, most of the time being weapons or armour or arrows but enough of their blood can lead to the construction of walls, bridges, doors, whatever they need really, in seconds, with the only risk to using too much of their blood being that they pass out and risk dying. They can circumvent the not-enough-blood-for-something issue by stockpiling solidified rods or some other shape of the stuff for later use, as the objects can be liquefied and reformed at will when in contact or even reabsorbed if they've lost some for some reason. Lost silver blood recovers as fast as normal blood so they can't simply recover in a short amount of time if no replenishable previously 'banked' source is available. They are not limited to the reabsorption, manipulation, or reshaping of their own silverblood, as there is a close enough relation to all silverbloods for them to be able to use that which was produced by other silverbloods.
If they lose contact with something made from their blood it becomes dull grey as well, but once contact is re-established it gains its gleam once more. Injury, age, and disease is not too much of an issue for silverbloods as they're largely immune to most pathogens, heal twice as fast with no scarring but are still susceptible to limb or organ loss, and seem immune to the passage of time as there are one or two silverbloods who are well into their second century without anything to them that could be described as 'old' except for grey/white/silver hair. Silverbloods can 'burn' an amount of their blood to produce a glowing mist that can perform tasks that a physical construct of their blood can't, like setting something on fire or freezing water, but they must take care with this ability as the burnt blood is lost forever until their body eventually replenishes it or they reabsorb a previously solidified object.
These boons are not without their drawbacks, as a silverblood is cursed with needing nearly three times as much food as a redblood, are heavier than they seem and have difficulty swimming, and have a tendency to not operate well under in hot conditions as their body heat is slightly higher than a redblood's. A rare occurrence, but if a silverblood was struck by lightning it's guaranteed for them to die where a redblood would at least have a chance of surviving.
The silver blood is inherited from parent to child in an excruciatingly painful rite of passage ritual where it feels like your very bones are on fire. The ritual does not work for people who aren't closely related, and if tried would kill if not severely harm the non-related recipient. What people don't know about the silver blood is that it's actually a collection of nanomachines performing all of the functions normal blood usually does in addition to the abilities it gives, and the sensations during the ritual are due to your bone marrow being replaced by factories for these nanomachines whose workings are imperceptible to the naked eye that also performs the bone marrow's usual duties as well.
The setting is 15th century medieval, but only technologically/socially due to it being a setting in which the world has recovered from an apocalypse that has effectively knocked the world back to the stone age. Advancement was faster than usual initially due to the survivors but as the generations went on only more immediately useful knowledge was passed on like tanning and woodwork instead of things that were currently out of their reach like electronics, causing a degradation over time of the overall knowledge-base of the population as a whole and kept the civilized world in a relatively low-tech state.
Accessible libraries with physical books who have miraculously survived the passage of time still exist but the language and script has changed and superstitions and fear has made people avoid any of the ruins and old buildings that dot the landscape. The only advanced technology they still have at their disposal and frequently use are the nanomachines of the silverbloods, but due to them not understanding it their outlook of it is on the mystical side of things, basically looking at silverbloods as if they were sorcerers.
They'd be able to construct much more powerful and devastating weaponry and near-indestructible protection with their nanomachines if they knew how, but that knowledge has been lost. The libraries are a hope for knowledge recovery but everyone avoids them and the ability to read what's in them isn't available so it's not like you'll have knights with laser/plasma weaponry and force field shields any time soon, and so they still fight with normal kind of weapons and armour, with anything made out of their blood being on par with what would be considered by 15th century smiths as high-quality steel work. One who has lost limbs or organs may even be able to produce cybernetic stand-ins, but still the lost knowledge point remains.
Their versatility and power has led to the majority of silverbloods finding themselves as part of some army's elite and more highly paid units as redbloods are seen as inferior and it being perceived as fact that they'd obviously make for much better soldiers than anyone else. The question on my mind is if they'd actually be better than a normal soldier or if the perception is wrong and that their 'blood' is as much of a hindrance as it is a benefit with regards to their weaknesses, their comparatively higher cost to maintain/feed, and 'medieval' level of power.
Would silverbloods actually make for better/superior soldiers?
Extra information as requested by A Rogue Ant:
- The blood's durability is varying depending on its state, with it being squishy and easily manipulated like mercury as a liquid but being as unyielding as forged steel as a solid.
- Other metals won't dissolve in the silver blood. The only way to have the blood dissolve other metals is through expending some of their blood to form the glowing mist which would then take something apart if they wanted it to. It's a one task per cloud kind of ability, the volume of the cloud determining the scale of the effects with 1 liter of silverblood spent/burnt creating a 1 cubic meter cloud.
- The fine-ness of their control is as fine as the clearness of their idea of what they want is. If they simply want a sharp sword they'll get one but how sharp they'll have no control over, but if they focus on wanting a sword with a 10 degree angle to its blade and 1 meter in length they'll get the 10 degree blade 1 meter in length, though a clear idea of degrees and measurements and the exact values of each is required. They can also emulate an already existing object to a 1% margin of error if they see the object while forming it and to a 5% margin of error from memory only.
- From puddle to longsword the process takes about two seconds.
- Things can be reformed on the fly but battle tends to be chaotic so any reformations will be inferior in quality due to shape errors to what they could've spent time on as to the object's specifics before the battle.
- Having some parts be more solid while others not for a semi-solid controllable assortment of multi-purpose tentacles from walking to manipulation at a speed similar to muscle limb movement, or as Ant calls it, "Doc-oc", is possible but only if they train themselves to use their blood as such due to the high amount of mental effort required to constantly control it like that. This includes 'catching an arrow' if they were aware of the arrow in flight and could move a blood limb in time. Smaller and more finely-controlled silverblood limbs are also possible but takes more mental effort.