This article contains spoilers for the A Court of Thorns and Roses series, including A Court of Silver Flames.
Koschei has spent most of the ACOTAR series at the edge of the story: trapped beside a distant lake, influencing events through curses, bargains and other people. In A Court of Splintered Harmony, that is about to change.
The official description for ACOTAR 6 confirms that Koschei the Deathless is stirring. Although an ancient spell still binds him to a mountain lake, his influence is spreading through the Fae territories. Powerful allies are gathering around him, and their target is clear: the human lands.
That makes Koschei more than another unfinished plotline from A Court of Silver Flames. He is the central threat facing Prythian in the first book of the Valkyrie Cycle.
So what do we actually know about him? What does he want, how is Vassa connected to his plans, and what could finally set him free?
Who Is Koschei in ACOTAR?
Koschei is an ancient Death-God who lives on the continent. He is the older brother of the Bone Carver and Stryga, better known as the Weaver of the Wood.
According to the Bone Carver, all three siblings entered this world long before Prythian was divided into courts and before the first High Lords were crowned. The ancient Fae feared and worshipped them. Koschei and Stryga were also considerably more powerful than their younger brother—powerful enough that the Bone Carver chose to hide from them in the Prison.
Koschei is not a High Fae ruler or an ordinary sorcerer. Rhysand makes that distinction clear in A Court of Silver Flames: his power belongs to something much older and more dangerous.
For a fuller overview of his history and known appearances, you can also visit our Koschei character guide.
Why Is Koschei Trapped at the Lake?
Thousands of years ago, an unnamed Fae warrior managed to outsmart Koschei and bind him to a lake on the continent.She also played a role in containing Stryga, but she could not kill either sibling. They were too powerful. Imprisonment was the only victory available to her.
The exact terms of Koschei’s spell remain unknown. We do not know why the lake holds him, what would break the binding or whether he needs someone else to release him. What we do know is that the warrior’s bloodline did not disappear completely. The Bone Carver says a trace of it still survives in a human line.
That detail has been waiting in the story since A Court of Wings and Ruin. Now that Koschei is actively threatening the human lands, it may become much more important.
How Powerful Is Koschei?
The books have deliberately kept the limits of Koschei’s power unclear. Even so, the evidence we have is alarming.
Koschei can place complex curses, influence people far beyond the lake and plant ideas in distant courts. Vassa says he turned words into weapons, allowing suggestions to travel until they reached the human queens. Rhys also believes Koschei was capable of making a group of Fae soldiers disappear and either gave Briallyn the ability to winnow or moved her himself.
Most importantly, the lake does not make him powerless. It restricts his physical freedom, but it has not stopped him from building alliances or shaping conflicts beyond his prison.
The Bone Carver calls Koschei and Stryga Death-Gods. Vassa calls him Koschei the Deathless and says there is no death waiting for him. Whether that immortality has a hidden weakness has not yet been revealed. The last warrior who faced him could only contain him.
What Does Koschei Want?
His immediate goal is the clearest part of his plan: Koschei wants to escape.
As Vassa puts it, “Everything he does is to free himself.”
But freedom appears to be only the beginning. Vassa fears that, if Koschei sees the world weakened and divided, he will strike and attempt to make himself its master. She believes he has tried to do exactly that before.
The description for A Court of Splintered Harmony now adds a more specific target. The allies drawn to Koschei want to reclaim the human lands. That places the fragile human territories—and the peace established after the war with Hybern—directly in danger.
Koschei therefore seems to be working toward three connected goals:
- break the ancient spell that binds him to the lake;
- gather powerful allies while Prythian remains divided;
- seize control of the human lands and expand his power from there.
The books have not yet revealed how those pieces fit together. He may need the human lands for political control, for something connected to the surviving bloodline of the Fae warrior, or for an entirely different purpose. For now, only the threat to the lands themselves is confirmed.
Why Did Koschei Curse Vassa?
Vassa’s story is the most personal example of what Koschei can do.
The other human queens saw Vassa as a threat. They could not kill her without allowing an even more defiant heir to take the throne, so they turned to the ancient Death-God beyond the wall. Through their bargain, Vassa was sold to Koschei. He stole her away and placed her under a curse that makes her a human queen at night and a firebird by day.
Her father later negotiated a temporary release, which allowed her to leave the lake and fight in the war against Hybern. The bargain did not end the curse, however, and Koschei still regards her as his.
What he ultimately wants from Vassa remains unanswered. She may be a possession, a political tool or a necessary part of his escape. The series has not confirmed which—only that her freedom is temporary and her connection to him is unfinished.
Koschei’s Alliance With Briallyn
Briallyn was the first clear sign that Koschei could operate far beyond his lake.
Vassa explains that the human queens did not find Koschei on their own. He planted words in their courts and allowed those words to travel on the wind. By the time they offered Vassa to him, they were already acting inside a plan he had set in motion.
In A Court of Silver Flames, he later supports Briallyn’s campaign against Nesta and the Night Court. Rhys identifies him as the likely source of her new abilities and the force capable of making her soldiers vanish. Briallyn may have believed she was using his power for her own revenge, but everything we know about Koschei suggests the arrangement served his larger goal.
Briallyn is now dead. Her death, however, did not end the threat behind her.
Is Beron Working With Koschei?
Beron is one of the most obvious candidates for the “powerful allies” mentioned in the new book description—but his role is not yet confirmed.
In A Court of Silver Flames, Eris reveals that Beron pledged his forces to Briallyn and personally met with her. Because Briallyn was working with Koschei, this places Beron dangerously close to the Death-God’s network.
It does not prove that Beron knowingly serves Koschei. He may have understood exactly who stood behind Briallyn, or he may simply have seen her planned war as an opportunity to gain power. Until A Court of Splintered Harmony answers that question, Beron remains a strong suspect rather than a confirmed Koschei ally.
Why Koschei Is the Main Threat in ACOTAR 6
The official description of A Court of Splintered Harmony removes any doubt about Koschei’s importance. He is stirring, his influence is spreading and his allies are preparing to move against the human lands.
The timing could hardly be worse.
Prythian is still recovering from the war with Hybern. The courts are not fully united, old alliances have weakened and the Night Court is dealing with betrayals and newly revealed truths. Koschei does not need to overpower a united Prythian if he can exploit the divisions already tearing it apart.
That may be the real meaning of his “creeping shadow.” Koschei’s greatest weapon has never been a direct attack. It is his ability to whisper, bargain and push other people toward the choices that benefit him.
To stop him, the Night Court will have to repair its own relationships and rebuild former alliances. That makes the external conflict with Koschei inseparable from the fractures within the group itself.
Why the Valkyries May Be Crucial
A Court of Splintered Harmony is also the first movement of the Valkyrie Cycle. That title makes it difficult to imagine Nesta, Gwyn and Emerie remaining on the edge of the conflict.
The Valkyries were rebuilt from a history that had nearly been erased. Koschei, meanwhile, is a threat from a time so ancient that even the courts did not yet exist. A confrontation between them would connect the newest power in Prythian with one of its oldest enemies.
Nesta’s connection to death may also matter. She took power directly from the Cauldron, created the new Dread Trove and has already killed both the King of Hybern and Briallyn. None of that proves she can kill Koschei—but it does make her one of the few characters who may be able to challenge what everyone else calls deathless.
That remains a theory, not confirmed plot. The official description says the Night Court must confront Koschei’s growing threat, but it does not reveal who will face him directly or what role the Valkyries will play.
Can Koschei Be Killed?
Right now, the honest answer is that we do not know. Vassa believes Koschei is truly immortal. The ancient Fae warrior who defeated him was unable to kill him and resorted to binding him instead. Those facts make a conventional death unlikely. They do not necessarily make him unbeatable.
ACOTAR repeatedly turns old stories, forgotten bargains and hidden names into weaknesses. Koschei’s prison was created through an ancient spell, and the bloodline of the warrior who trapped him still exists somewhere in the human world. Either detail could offer a way to strengthen his binding—or finally end him.
For now, any more specific answer would be theory rather than canon.
The Biggest Koschei Questions ACOTAR 6 Must Answer
The books have established enough about Koschei to make him dangerous, but they have left the most important parts of his plan hidden.
- What can actually break the spell around the lake?
- Who are the powerful allies gathering around him?
- Does Beron know he may be helping a Death-God?
- Why does Koschei want Vassa specifically?
- Which human family carries the Fae warrior’s bloodline?
- Can Nesta’s power harm someone who is supposedly deathless?
- Will stopping Koschei require killing him, imprisoning him again or making a new bargain?
Koschei has been preparing for freedom while the rest of Prythian has been recovering from war. He cursed Vassa, manipulated the human queens, empowered Briallyn and built influence without ever leaving his lake.
Now the official description of A Court of Splintered Harmony confirms that his shadow is spreading and the human lands are in danger. The Night Court will have to confront him while it is fractured—and before his allies can turn those fractures into another war.
Koschei may be bound, but he has never truly been contained. ACOTAR 6 is where the difference finally matters.
Frequently Asked Questions
Who is Koschei in ACOTAR?
Koschei is an ancient Death-God and the older brother of the Bone Carver and Stryga, the Weaver. An ancient Fae warrior bound him to a mountain lake on the continent thousands of years ago.
Is Koschei the villain of ACOTAR 6?
Koschei is the central external threat named in the official description of A Court of Splintered Harmony. The full extent of his role and the identities of his allies have not yet been revealed.
Why is Koschei called the Deathless?
Vassa says that no death awaits Koschei and describes him as truly immortal. The ancient warrior who defeated him could not kill him and had to imprison him instead.
What did Koschei do to Vassa?
Koschei cursed Vassa to live as a firebird by day and a human queen by night after the other mortal queens sold her to him. Her father secured only a temporary release from his lake.
Is Beron allied with Koschei?
Not officially. Beron pledged his forces to Briallyn, who was working with Koschei. This makes him a likely candidate for Koschei’s network, but the books have not confirmed that Beron knowingly serves him.
Can Koschei leave the lake?
An ancient spell currently binds Koschei to the lake. He can still influence events and people elsewhere, but he appears unable to leave physically unless the spell is broken.
Can Koschei be killed?
The series has not revealed a way to kill him. He is described as truly immortal, and the Fae warrior who once defeated him could only contain him.
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