Something - whether it's a tool, a weapon, an accessory, etc. - can be made out of regular iron, of silver, of Thunderbolt Iron... this one's metal came from an unusual, yet completely real source.
The blood of many advanced organisms contains iron. Theoretically, something could be made out of it. Of course, there is a good chance the source of that blood will die. Perhaps many will die. After all, there are only a few grams of iron in a person's blood. As such, the item made in this way will likely be evil (as Blood Magic tends to be).
Related is the idea of quenching a newly-forged blade in blood, possibly by stabbing it through a living body, which is said to give it a soul. This absolutely would not work in real life.
A variant of characters who manipulates/uses blood as a weapon is one where they can create stuff (usually weapons) with the iron from the blood, whether it's theirs or from other people.
- Jo Jos Bizarre Adventure Vento Aureo: Risotto's Stand, Metallica, is capable of manipulating iron, including the iron present in the blood of a person. Being an Mafia assassin, his methods aren't pleasant to watch; those unfortunate enough to be within Metallica's range will find themselves coughing out razor blades from their throats, and will discover all sorts of sharp, nasty objects protruding from their face and neck. This way, Risotto can eventually cause his victims to die of suffocation by robbing them of the iron needed to transport precious oxygen, to the point their blood turns yellow.
- Naruto: Long after its introduction, Zabuza's sword Kubikiribouchou is revealed to have the power to repair itself by drawing iron from the blood it spills.
- Fullmetal Alchemist: Edward makes a sword for Ling from the iron in the massive amounts of blood in Gluttony's stomach.
- In X2: X-Men United, Magneto escapes his prison by ripping the iron out of a guard's blood and fashioning it into a couple of pellets. Most of it is an iron solution Mystique injected into the guy earlier, but some would have been his own.
- In Making Money, there's a rumor that the blade of Lord Vetinari's Sword Cane is made from the blood of a thousand men. Given that Vetinari is the pragmatic sort, it's unlikely to be true. Well, it's actually not even clear whether it actually contains a sword, or if it's just one of the many rumors surrounding him. In any case, it's deadly enough in his hands as a stick.
- In the Whateley Universe, Bloodsteel, both due to the name and the description of something with a hell of a lot of bloodsteel, meaning "far too many people died in the process" of its creation, implies that blood is a component. It is not quite clear what it actually is though.
- In The Gates of Hell, the archdevil Sammael carries a rapier made out of iron drawn from the blood of thousands of humanoid creatures. It suppresses the healing of anyone struck by it. Marks of the Dark Ministry are Blood Iron as well.
- Azure Striker Gunvolt 2: Gibril's Septimal power, "Metallon", lets her manipulate metals. She usually uses blood as her source of iron, whether taken from draining people's blood or (when she's desperate enough) her own.
- The Bloodborne DLC The Old Hunters adds a new weapon to the arsenal, a mace called Bloodletter. When switching it to its alternate mode, the wielder must plunge the sharp end into their own chest, drawing massive amounts of blood, which then forms into a new, much larger and much spikier mace head made apparently out of their blood iron (because of how blood magic works in this universe, this action only causes the character to lose a handful of HP).
- In Guilty Gear, Testament's scythe has a blade made of hardened blood iron.
- Skarlet from Mortal Kombat practices Blood Magic and during the pre-fight banter with other characters, is often shown fashioning blood into a knife or other type of blade.
- Allegedly, in the 19th century, one chemist, or student of chemistry, attempted to make a ring out of his own blood's iron as a gift to his beloved. He died of anemia before it could be completed.