Name: Kuronuma (Literally ; Black Swamp) Clan
Village(s): Originally from within The Land of Water, like many obscure clans from this area it revolted and was chased out into the Land of Fire.
Kekkai Genkai/Bloodtrait: The "Iron Swamp" technique. Members of the Kuronuma clan have blood that is especially receptive to chakra, and quickly oxidizes once outside of the body. This allows for their blood to be substituted for water in most jutsu with caustic results (Burning of skin, rusting of weapons).
In particular, the Kuronuma Clan has adapted the popular "Hidden Mist" Jutsu from their homeland into a more advanced technique they call "Ketsueki Kiri; Tetsu Numa" (Bloody Mist; Iron Swamp).
This technique can only be used once a month, twice if perfected, due to the amount of blood lost from the user. The area is quickly surrounded by a red fog that starts to rust anything inside of it, even humans, while the caster moves around and performs the Silent Killing technique like usual.
Unlike the regular Hidden Mist jutsu, which only fools Sharingan and Rinnegan, the Bloody Mist is capable of fooling the Byakugan due to it effectively spreading the user's body across a large area.
Background: Much of the history of the Kuronuma clan is wordless and barbaric, paralleling the Kaguya clan until its fall. Like many of the rogue clans of the Land of Water, the Kuronuma ninja had insatiable bloodlust. This led to a revolt against Kirigakure in which the clan was ultimately defeated and exiled. Many members of the clan, more than half of them, died in the fighting. The rest fled to the Land of Fire.
Their knowledge of Mist techniques, especially their adaptation of the Hidden Mist; Silent Killing combination, led to many of the remaining clan members being distrusted as cold blooded assassins. Many elect to become rogue ninja due to the distrust they face in their new home, becoming killers for hire, while others still find their place among elite tracking taskforces such as Konoha's Anbu squads.