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.
  • $\begingroup$ "Their versatility and power has led to the majority of silverbloods" in all the content of the question, I haven't heard anything about their of physical power/strength, their agility or endurance. The fact that can construct a walls/bridges of steel-like hardness is not as valuable as the speed they can do it, a fact that would relegate them more in "engineers corps". But,are there enough of them for some non-trivial amount of walls/bridges? 8 liters of silverblood (double, ok, triple that with reserves) it's not that much. $\endgroup$ Nov 24 '21 at 12:16
  • $\begingroup$ Bottom line, most of the wars are won or lost by the logistics. So, can they do more than the 3 redbloods they eat for? $\endgroup$ Nov 24 '21 at 12:18
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    $\begingroup$ BTW, higher body temperature means they will perform better in hot weather then their redblooded counterparts. Because they are used with being hot. Or, in physics terms: everything being equal, the heat flow is proportional with the temperature differential, they'll have less troubles pumping heat outside. $\endgroup$ Nov 24 '21 at 12:38
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    $\begingroup$ @ARogueAnt. Requested information added $\endgroup$
    – Lemming
    Nov 24 '21 at 13:39
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    $\begingroup$ I'm already pretty convinced that the perception of their superiority is well-founded, but I'll give the information to your questions anyway. There's at least one family of silverbloods per large village. Redbloods generally know silverbloods can make armaments suddenly appear but as for everything else their knowledge only goes as far as written/verbal accounts and personal experience. The only training redblood soldiers receive against silverbloods are actual battle experience or from sparring with a silverblood who is part of their own army. @ooak $\endgroup$
    – Lemming
    Nov 26 '21 at 7:19

Internal control:

As a biologist, I always see things as an interplay of conditional advantages and disadvantages. I am a big fan of nanites as the rationale for pseudo-magic. What I suspect is that the way to use these abilities best would be to figure out how to make the most of the nanites while they're still in the body.

For external use, I think the key (and yes, this would be perfect for keys) would be practice. There are no nerves in the fluid, so they get limited feedback. A fighter will get the feedback from a knife, a thief the feedback from a lockpick. use easy shapes, or create small observable parts. The biggest use in a fight is surprise - the knife in the hand of the unarmed, for example. In this case, carrying extra rods of blood will be a dead giveaway.

  • If you want external armor that's adaptive, you will need to spend weeks to months gathering up the excess mass that will mostly be a substitute for conventional equipment. Your ability to spontaneously alter and repair this equipment will be helpful, but not as big of an advantage as you might think. But a sword suddenly becoming a spear would be really useful. Then the head explodes like a pufferfish inside the wound - nasty.
  • Concentration will likely be a bigger problem. People think a lot less than you give them credit for, and your warriors would need to devote a lot of concentration to shaping and maintaining equipment. The may be better off with normal weapons enhanced with this ability (like a thin external coating allowing better control).
  • Since it's precious, and hardens externally, don't build a bridge with it, make the nails, or the joins and clips.
  • I don't know if you can induce rapid motion (like drilling) but if you can, there are other interesting abilities that allow you to replicate modern equipment. I would avoid this one, but it's your story.

But in terms of blood volume, the issue will be weakness and endurance. Armor will move so much blood outside of the body as to make the character too weak to fight well. You can't function well way before you reach the point you die from blood loss (that's 18 years of blood-banking talking). This stuff must weigh about as much as metal for it to work like metal, and from a biological point of view, it must eventually start to attenuate separated from flesh (I'd suggest about thirty days, if it behaves like a unit of blood taken from the body).

Keep the stuff inside where you'll have the best control.

We've already established that they greatly increase healing. In this case, I think you're trying to make hemi-metal terminators, so I'll make the comparison for what it can do according to that (although the shape is maintained after dissociation with the body). I'm assuming the fluid can be drawn back into the body after being extended out of it (recovering blood volume).

  • Use the blood to harden the flesh to metallic consistency when hit. The epidermis will get nicked up with cool scars, but otherwise armor can be INSIDE the body.
  • Similarly, shift weight telekinetically to increase the strength of blows.
  • Besides rapid healing, simply don't bleed! You control the blood, so it will stay in the body even when you're injured. Solidify a little at the site of a "lethal" killing blow and that cut artery is a minor inconvenience. Between this and disease immunity, your warriors need to be decapitated or pinned down and systematically chopped into pieces to kill them, so as long as they aren't grossly outnumbered, they are very hard to kill.

Big Advantage

One of the major ways a soldier is killed in ancient/medieval combat is through blood loss. An artery gets cut, and they bleed out within seconds/minutes and die. Or minor injury/ies weakens them, and they get killed because the blood loss slowed them down. Silverbloods can survive both these problems with ease. Either they A: simply order their blood to instantly coagulate (not sure of the feasibility of this in your setting so this may only work for minor wounds) or B: they can replenish their blood supply via stored rods. Either way, they can take injuries and blood loss that would kill a normal human and keep on fighting, at least for a while. That's a huge advantage.

The other big thing is they can in theory have variable-length weapons. Imagine your Sivlerblood is equipped with a 8ft spear (the traditional fighting weapon, swords were almost always backups) with a silverblood head and a fine line of silverblood running down the length of the shaft such that the user can always be in contact with it. You stab your opponent, and he jumps back. At the same time you activate your silverblood spear and increase the length of the blade another foot, which catches and kills him. This also works with swords, or even shields. Yes it takes a second or two to go from "puddle of liquid" to "hard as steel" but that in-between state should be more than enough to pierce flesh or knock aside a blow. Especially if the growth/change is imparting some extra kinetic energy to the weapon/shield. Hell, you could even use it to blind enemies in full helmets or jam joints in plate armor.

If your soldiers have time you could also do some pretty cool things with their personal armor. variable-density breastplates with a hard outer shell and a "squishy" liquid middle to absorb kinetic impacts for example. I don't think they'd be that more effective than simply wearing "normal" armor with quilted gambeson etc, but it could be part of their mystique and may end up weighing a bit less, which would be nice.

For added fun, they'd be able to have emergency DIY caltrops. Not a war-winner by any means, but if they had a rod of blood set aside for it a unit of silverbloods would be that much more difficult to tackle when defending.


Silver blood = silver TANK

The way you describe, these people are at the center of a nanotech machinery empire. One that can be implemented as a tank that sounds reasonably comparable to modern steel (maybe not depleted uranium) in terms of armor, but which has unorthodox features such as the ability of its tracks to spear fish people and drag them under to be crushed. They can certainly extend and reshape (at the cost of less armor) to become trebuchets with buckets custom-shaped to work with each boulder they encounter on site, or which can be dug from the ground with silvery tentacles. They can worm into cracks and expand like the frost of a hundred winters to tear apart any masonry, and pass beneath a breach in any wall while holding it up and leaving steely supports behind that can be collapsed at will if the wrong folks follow.

Basically, your Terminator 2 is going to chew up the enemy army quite nicely. More than one would be overkill ... but what military doesn't like overkill?


If they need to be in contact with their silverblood to control it, they can't really make arrows or any projectile weapon out of it.

For once, they would need a string attached to it to control its flight, and they would be stuck in recovering it before a new use. Not really handy, especially if your target is not the standard NPC waiting for you to do as you please, but is actively trying to cut that string and leave you unarmed.

Moreover, a human body contains about 5 cubic decimeter of blood, or 5 liters, not much wall or bridge can be done with it.

In short, if any advantage can be found in these silverblood, is in close range combat, where they might parry attacks from any direction as long as they can protrude the mass out of their body.

Oh, since we are talking medieval times, wars in those times were preferably fought in summer, meaning that the higher temperatures might put your silvebloods at a slight disadvantage.

  • $\begingroup$ " 5 cubic decimeter of blood, or 5 liters" between 7% and 10% of bodyweight. Say 8l tops and you're covered. $\endgroup$ Nov 24 '21 at 12:34

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