Bloodthirst is an Akaviri "blood drinker" longsword, the other known example being the transforming blade, Dawnfang and Duskfang. Another enchanted longsword, Rimelink, is crafted in the same style as these weapons.
Like Dawn/Duskfang, its crossguard and pommel are adorned with elegant jewels, its pronged blade resembles the gaping maw of a beast, and it has a snakeskin pattern that envelops the areas around the crossguard, handle, and pommel. Like Dawnfang, it has a golden snakeskin pattern, but it differs from both Dawnfang and Duskfang in that its jewel is infused with swirling red blood. Its sinister appearance is known to make people feel uneasy. It earns its name thanks to its unquenchable thirst for blood, and it fortifies its wielder and increases their swing speed.
Sometime after the end of the Great War in 4E 175, the former member of the Blades, the Warrior, came across Bloodthirst in their journey. The method of acquisition of the sword is conflicted, however.
The sword similar to Bloodthirst, Dawn/Duskfang, was at one point acquired by Lorant Bouchard, an infamous Blades captain who was rumored to be a serpent. The death of his wife Emma, and the sword's influence combined to weigh down on him, causing him to fall further into madness and begin taking out his suffering on others, and to begin dabbling in necromancy. In 4E 130, the necromancer Sychelle Gatharian hired a group of mages under the guise that they were to capture Lorant for his treachery. Their initial encounter with Lorant failed miserably and they were forced to retreat. They found his experience as a swordsman in combination with his sword, and his ability to resurrect those he killed overwhelming. The mages realized that to defeat him, the best course of action was to somehow separate him from his sword. Sychelle made preparations to fund a second attempt to capture Lorant. She hired a group of smugglers to aid the mages in fulfilling their contract, and revealed her hidden motive to the their boss, Verrick Tilwald. She had in her possession Bloodthirst, and revealed that the capture mission was a front to obtain Dawn/Duskfang and swap it with Bloodthirst. She insisted that he keep the plan a secret from the mages, and the deal was sealed with the exchange of a coin. Verrick had other plans however, and plotted to betray his mage allies and employer if they were successful with retrieving Dawn/Duskfang. Unfortunately, before he and his associates made the journey to fight Lorant, he lost Bloodthirst within Faldar's Tooth in the Rift.
With their plan finalized, the mages made their move and located Emma's remains. They relocated it to a vault in Riften's Ratways and intended to use it as a lure. Lorant tracked them down and intended to slaughter them for their audacity to disturb his wife, and upon his arrival the mages and smugglers sprung their trap. The mages were successful in separating him from his sword, sealing it behind an impenetrable barrier in the vault's central chamber. Unfortunately, something interfered with the separation spell, and its unintended effect divided Lorant into three different hostile spirits. Several theories of what lead to this unfortunate event emerged. One mage concluded that the spell failed because magic is inheritably unpredictable,  while another theorized that the sword may have an ability to interfere with magic. Verrick was the one most to blame. He noted that his incompetence led to Bloodthirst being lost, causing a significant divergence from the plans Sychelle laid out for him. Sensing their imminent demise, the mages worked to binding Lorant into three different areas of the vault, and summoned Emma's spirit in hopes of using her to convince her husband to calm down. The little time they had left allowed them to successfully complete the binding ritual, but at the cost of all but one of them being sealed inside with the vengeful Lorant. As Verrick waited for his demise, he realized that the coin Sychelle had given him had been cursed, perhaps indicating how his greed led to his downfall. Lorant remained within the tomb as its prisoner, and as the guardian for the sword and his wife's remains; all who entered the tomb were killed by him. 
In 4E 201, the Last Dragonborn investigated Riften's Ratways after hearing rumors of disappearances and ghost sightings. Within the Ratways, The spirit of Lorant's long departed wife, Emma, manifested and guided the Dragonborn through Lorant's chambers. The Dragonborn defeated Lorant's fragments and made him whole, finally freeing him and allowing him to reunite and rest with his wife in the afterlife. With Lorant free, the barrier surrounding Dawn/Duskfang was removed, allowing the sword to be retrieved. After obtaining the blade, the Dragonborn discovered a note within the vault detailing the long departed Verrick's deal with Sychelle, as well as the last known location of Bloodthirst. Upon learning this, the Dragonborn ventured to and cleared out the bandit that had taken residence in the ruins of Faldar's Tooth. It was too late, and the acquired intel noted that the bandits had sold it to someone who had taken residence in Broken Fang Cave. The Dragonborn discovered that the people who had taken interest in the sword were vampires, and eradicated all the inhabitants of the cave. The Dragonborn then retrieved the sword.
- A Soul Divided quest in Skyrim
- Events of Blades
- Sellonus's Journal Vol. 1 — Sellonus
- Sellonus's Confession — Sellonus
- Verrick's Note — Verrick Tildwald
- Old Smuggler's Note
- Sellonus's Journal Vol. 2 — Sellonus
- Guild Mage's Warning
- Guild Mage's Note
- Guild Mage's Missive
- Sellonus's Journal Vol. 3 — Sellonus
- Cage Bandit's Note