Being one of the 13 artifacts The Blood Sword is an old item. At its forging, a shaman summoned up a demon and then captured its essence, then shackled it to the blade. The blade brings great power at the cost of hunger for carnage, the wielder is bound to the blade and compelled to sate its hunger.
Being passed from one to another, Blood Sword wielders have clashed with Witchblade wielders in the past, one such event was Japan in 1635 when Shiori-sama had passed on her Witchblade. The Blood Sword's wielder was tasked to retrieve the Witchblade, but she was defeated and killed. The Blood Sword moved on to another wielder. It is unknown what happened to it, but it again surfaced in Japan in the hands of one samurai, he was soon betrayed by his own ally, and the sword was stolen.
Sometime later a new bearer used the power of the Blood Sword to become a warlord. The warlord was ever vigilant to watch out for betrayers. The symbiosis between the two was even stronger than before as the sword craved blood the warlord supplied it and received power in return. The warlord's spirit endured long after his body became dust due to the symbiosis.
Kenshin Kawakami is one of the confirmed past wielders.
The Blood Sword then slumbered until it woke in New York, It again clashed with the current Witchblade wielder, Sara Pezzini. Sara defeated the Blood Sword in battle and released the samurai spirit; she then took the sword to the Curator where it was held until Ian Nottingham stole it and used it to exact revenge on some Yakuzas hunting him. When Ian was arrested, the Blood Sword was returned to Curator's care.
During the events of the Broken Trinity story, Patrick Gleason brought the sword to battlefield, and stabbed Angelus. Next; Jackie Estacado used the sword to decapitate Angelus, thus killing the host, and leaving the Angelus to seek another. The Blood Sword is then given to Michael Finnegan along with the Scroll of the Thirteen, who then goes on to search for the balance between stone of Ember and Glacier. The sword is a reason why Finnegan started to learn the way of katana.
During the gathering of the 13 Artifacts, Ian Nottingham was ordered to steal the sword from Finnegan and he was successful. Ian now the Blood Sword wielder joins the side that wants a new world order.