Name: Oni Sutemi
Properties/description: A katana made of an alloy constructed of titanium, seastone, and a rare mineral, Indigite, which has a particularly strong affinity to seastone along with a few select metallic substances.
The mineral is melted and mixed with crushed seastone and then and then added to titatium that has been melted at 3035F
During the construction if this particular sword the titanium was melted in a forger, the indigite was melted by hand in a crucible by means of a friction devil fruit and kept in liquid by applying more devil fruit induced heat to keep the mixture hot a liquid while the seastone powder is mixed in. This creates a sword that is black as midnight with an iridescent blue sheen.
Abilities: The titanium makes this sword stronger and lighter than any other material and and also makes the blade immune to oxidation and magnetic fields. The mineral and seastone further fortify the sword making its strength only matched (not surpassed) by diamond, and thusly never dulls. Due to the seastone within the the blade, it is particularly effective against devil fruit users, however, the hilt is fortified to make the blade wieldable by devil fruit users but due to an unfortunate incident during its creation, the sword will only tolerate on master.
(Also, a vicious, ferrel bloodlust explained in the history.)
History:
Indirectly heating the liquified mineral, through the crucible, in contact with the seastone had very adverse effects on the blacksmith devil fruit user creating the blade. Working in opposition to the stone via indirect heat causes the bizarre physical effect of internally crushing capillaries or sometimes worse. This blood was coughed up by the black smith while the sword was still hot-hot and instead of the blood simply being vaporized instantly as expected, it was absorbed into the sword, giving it a very dark crimson swirls. The sword had seized a blood sacrifice for itself, nearly killing the black smith in the process, and gained a very wicked blood lust after absorbing so much blood from its creator. Only the blacksmith was able to wield the blade, however, the cruel blade sought to destroy even the allies of the black smith, and so it was wrapped in bandages like a mummy, worn other the back of the blacksmith, tucked behind the sheath of a scythe, never to be used again. The cruel bloodlust of the blade was alway felt by the blacksmith constantly, looming ever darker, like a demon on her shoulder, begging to be released. She keeps the blade nearby to remind her of her quest to recreate harness the power of indigite alloys.
Only two swords she's made with indigite have asked for blood payment in return for their strength and these two are by far the most dangerous. These blades have chosen their masters, however that does not mean that they will be tamed by their master's without a fight.