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Urithiru by Elisgardor.jpg
Parents Honor, Cultivation
Abilities Nahel bond, Bondsmith magic, Splinter of Honor and Cultivation
Bonded With Navani, Melishi (formerly)[1]
Species Spren
World Roshar
Universe Cosmere
Featured In The Stormlight Archive
This page or section needs to be updated with new information for Rhythm of War!
Be aware that in its current state, it may not include all additional content yet.

There is ... a third sibling. They are not with us.

—The Stormfather[2]

The Sibling is a notable spren on Roshar.[3] They are of the same power level as the Stormfather and the Nightwatcher, and is the third spren historically associated with the Order of Bondsmiths.[4][5] The Sibling manifests physically as many fabrials within the tower of Urithiru and has control over them, with the crystal pillar being the heart.[6] They are currently bonded to Navani Kholin.[4][5]

Attributes and Abilities[edit]

The Sibling is known to have been alive for at least four and a half millennia and is functionally immortal.[2] The Sibling does not view themself as having a gender and finds the notion that spren do ridiculous.[7][8] Despite living thousands of years, they remain somewhat naïve. Oathgate spren follow the orders of the Sibling and refer to the Sibling as a parent.[9]


The Sibling is capable of producing their own Investiture known as Towerlight, a mixture of Lifelight and Stormlight, which they use to power the fabrials in Urithiru.[10] They need to be able to harmonize the rhythms of Honor and Cultivation in order to produce Towerlight.[4]

Nahel Bond[edit]

The Sibling is one of the three great Bondsmith spren.[3] Forming a Nahel bond with them grants one the power over the Surges of Tension and Adhesion.[11] While a Bondsmith can use Adhesion the way a Windrunner would,[12] they can also apply their powers in different manner, using them more in the Spiritual. Using Spiritual Adhesion, a Bondsmith can form a Connection between themselves and another person, allowing them to speak their language.[13] They also seem capable of hearing the spiritual aspects of objects and using this to mend broken things back whole.[14] Navani is able to assist the Sibling in once again making Towerlight in large enough quantities to fully restore the functioning of Urithiru.[4]

In order to bond with the Sibling, a person must be touching their crystal pillar.[10] The Sibling knows how to end the Nahel bond, and has done so in the past.[15] While the Nightwatcher and the Stormfather are known to be connected to Cultivation and Honor respectively, the Sibling is the child of both Honor and Cultivation, created specifically to oppose Odium.[16] The Stormfather considers all three of them to be "siblings", and the fact that they are the only three spren that can bond with Bondsmiths[17] indicates that they share some characteristics.


She saw the tower now as an entity, with lines of garnet very like veins and arteries. And she inhabited that entity. It became her body. She saw thousands of closed doors the scouts had missed in mapping the tower. She saw brilliant mechanisms for controlling pressure, heat — No, stay focused.

—Navani Kholin[6]

The Sibling is essentially the Tower of Urithiru and controls the many fabrials within.[6] They are capable of manifesting in the Physical Realm as both metal and as Polestones. The Sibling can also fully power and control every fabrial that makes up the tower.[18] The temperature becomes warmer since heating fabrials become more potent, for example.[5] ​The Sibling is able to see everything within the tower.[1][6] Their Bondsmith is also able to do so, as well as comprehend the mechanisms of Urithiru and speak through the veins of garnet in the tower as the Sibling does.[19][6]

The red garnet vein within the wall strata serves as means of communication.[20] It can light up and, upon being touched, the Sibling will be able to mentally speak with a person or spren,[21][22] although this can be eavesdropped through unknown methods.[23] This also allows people to communicate with each other if they are both touching the garnet vein.[8] The Sibling can also talk to people in weak mental state.[8] The line of garnet will give off a small amount of light when the Sibling wants it to.[24][25] This can be moved within the garnet veins to guide people.[1][26] The Sibling can open, close or lock the fabrial doors in Urithiru.[21] They are even able to key them to certain people.

The tower is very bright and due to the highly Invested nature of the tower, it glows brightly in the Cognitive Realm, making it hard for people to see specific spren while there.[20][6] Its highly Invested nature also makes it near impossible for the detection of kinetic Investiture.[27] Voidspren are unable to remain invisible while in the tower, though regular spren can.[10][28] Previously, the outer halls of the tower were coated in aluminum.[29]

Without Towerlight

When Ba-Ado-Mishram was imprisoned, the Sibling lost the rhythm of Towerlight, which stopped most of Urithiru from functioning.[8] In this state, the Sibling was only able to see patches of the tower and a small area around people who are Connected to them, mainly the Radiants.[1][8] Without hearing the correct rhythms, their Bondsmith would also be unable to produce Towerlight.[10] If the Sibling cannot generate Towerlight, they will be left open to be corrupted by Voidlight and Odium's tone.[8]

Without Towerlight, most of the fabrials were dysfunctional.[30][31] Functioning fabrial systems include those for increased pressure,[31] temperature,[32] and general conditions encouraging plant growth.[31] Navani also theorized that the air circulating through various shafts was powered by some sort of fabrial.[33] In addition, the fabrial elevators connecting Urithiru's floors begin running when gemstones were inserted.[34] Basic suppression of Fused powers remained active.[29] Gemstones to open walls still worked if infused with Stormlight, though the Sibling could not keep certain people from opening it, only able to lock or unlock them.[35][21]

Crystal Pillar[edit]

Deep inside the tower, there is a large monolith crystal pillar that serves as the Sibling's heart.[6] It is made of thousands of different gems.[36][37] The pillar is where the Sibling is most exposed, and is where they can be bonded or corrupted.[36][10] While functioning normally, the pillar glows the color of Towerlight.[36] If the Sibling is being corrupted with Voidlight, the color will darken.[38] The Voidlight and corruption can be pushed out by the rhythm of anti-Voidlight.[4]

In order to protect the crystal pillar, Melishi created a system of four sapphire fabrial nodes that produce a blue barrier around the pillar.[24][1][39] The barrier is strong enough to stop humans, singers, and even Unmade from breaching it.[1] It even has a way of silencing itself to Fused.[27] It can also be used to corrupt and unmake the Sibling remotely by infusing the nodes with Voidlight.[1] Since it was added later, the fabrial does not connect to the entirety of the tower and is powered by Stormlight instead of Towerlight.[1][27]

The shield is made using the Surge of Transformation; Soulcasting air and persuading it that it is glass.[8] When attacked, the section of the shield will evaporate and will then restore itself almost immediately.[39] Each node is accompanied by a glass globe, wrapped in metal wires.[40] The globes have a reproduction of the crystal pillar room inside them, which helps the Soulcasting think the air around it is glass.[39] This makes the Soulcasting not a full transformation, but more of a half transformation. It needs a constant stream of Stormlight via the nodes to keep functioning, and takes in much more than a typical fabrial of its size.[8][1] If a node is destroyed, the shield will weaken.[24] The more it is weakened and corrupted, the more its color goes from bright blue to dark violet.[41] If all four are destroyed, the shield will be destroyed.[8][38]

The first node was located close to the pillar and was destroyed by Navani.[1][8] The second node was built near the second level of the tower, so it can easily absorb Stormlight from highstorms.[28][40] It was destroyed by Kaladin.[40] The third node was in the center of the Breakaway market on the first floor.[10] It was hidden in a well near the pump mechanisms and was destroyed by Kaladin.[22] The fourth node was hidden in the infirmary room, inside the model of the tower.[38] It was destroyed by Moash. More nodes were meant to be installed, as well as higher up into the tower, but Melishi did not have time to do so.[10]

Suppression Fabrial[edit]

The Sibling has a large suppression fabrial built into Urithiru, much more powerful than a normal one.[20] It is built into a construction of garnets and destroying them will remove its effects.[42] It normally incapacitates Fused, Regals, and Unmade while inside its range.[43][6] Some of the Unmade are able to resist the effects, as well as other highly Invested individuals.[24][43] This fabrial can have varying power levels, from merely stopping some of the Fused from Surgebinding to knocking them unconscious.[29] When in effect, rhythms are disrupted.[20]


If the Sibling is corrupted, the suppression fabrial can be inverted, instead incapacitating Radiants.[43][36][8] While in effect, Radiants inside of the range (roughly hundreds of yards from the tower) will fall unconscious.[44] Their spren will also be pushed back into the Cognitive Realm, put into a deep sleep-like state.[20] Those who have bonded a dead Shardblade will be unable to summon it, though an unbonded one will remain unaffected.[45][46] The suppression fabrial also greatly limits the Stormfather's ability to see the tower and will inhibit his visions.[45][47]

If a Radiant is far enough in their oaths, they may be able to resist the effects, as well as keep their spren in the Physical Realm.[43][24] Those able to resist will instead feel an external oppressive pressure of darkness.[20][22] They are still able to take in Stormlight and it will continue to heal them.[48] The worse the corruption of the Sibling, the weaker the healing gets.[39][22] If a Radiant is also a Regal, they will be mostly unaffected by the suppressor, even at the First Ideal.[49] Those using an Honorblade will still be able to Surgebind and summon their blade.[50][38]

Windrunners (due to their Surge of Adhesion being a true Surge of Honor) will remain less unconscious, instead shaking and having muscle spasms.[24] Those close to or above the Fourth Ideal will remain awake and will still be able to draw in Stormlight.[8][46] They are also able to pull their honorspren back into the Physical Realm, though they are unable to form a Shardblade for longer than a than a few seconds.[20][51] Their honorspren's radius that they can travel from the Windrunner also decreases dramatically, going from miles to only about a floor.[20] While their Adhesion Surge will still work, Gravitation will not.[20] Due to Adhesion not being affected, it is likely that a Bondsmith would have similar resistance against the suppression.[45]

Lift, due to her Old Magic, will remain conscious and can continue to produce Lifelight.[52][8] Wyndle also remained in the Physical Realm, but was unable to become a Shardblade. Lift is still able to use the Surge of Progression, but not Abrasion. Lift is able to heal other Radiants, waking them up.[53] If she doesn't re-heal them within at least ten hours, they fall back into unconsciousness.[54] Despite this, her internal healing worked as a regular conscious Radiant's would and can get worse the longer the Sibling is corrupted.[49]

Fabrials will stop working while inside the range of the suppressor fabrial.[24] Fabrials made from Enlightened spren will still work, but only with Voidlight.[55][39] The Oathgates remain unaffected, and can still be used by an Honorblade.[20][42]


My research into the cognitive reflections of the spren at the tower has been deeply illustrative. Some thought that the Sibling had withdrawn from men by intent—but I find counter to that theory.

—The third zircon in drawer 1-1 of the Urithiru gem archive[30]

Heraldic Epochs and Era of Solitude[edit]

The Sibling was capable of forming a Nahel bond. There could never be more than three Bondsmiths; there were long periods where only one existed, which might have referred to the Sibling's Bondsmith, as they were vital for Urithiru to properly function.[56] They were very particular with their bond, often spending years evaluating Bondsmith squires.[10]

The Sibling was the key to certain magical aspects of the tower city of Urithiru that served as the base of the Knights Radiant. Notably, the Sibling's presence was linked to the climate of the city, allowing the temperature to stay unnaturally warm given Urithiru's elevation. This allowed the Radiants to cultivate crops in the city to sustain the large population there.[30][31] At some point, the Sibling began to withdraw from the tower. The Sibling's withdrawal caused some—but not all— of the city's magical systems to fail; it soon became uninhabitable, and the Radiants were forced to abandon the city.[57][31][58] It is not clear why the Sibling disengaged with mankind; an Elsecaller who left notes in the gem archive argued that the spren's disappearance was neither intentional nor a result of internal strife among the Knights Radiant.[30][31][59] The Sibling was wounded by the imprisonment of Ba-Ado-Mishram; this wound resulted in the Sibling losing the rhythm of Towerlight, which in turn stopped Urithiru functioning.[8]

After the Sibling's departure, they were not hiding but rather "slumbering" in the millennia following the abandonment of Urithiru and the Recreance.[2] The Stormfather has generally been reticent to discuss the Sibling with Dalinar because they were somehow harmed by mankind in the past.[17][2]

True Desolation[edit]

The Sibling first made contact with Navani Kholin through a purposefully placed spanreed ruby.[60] Initially, Navani and the Sibling were at odds due to their differences in morals regarding fabrial technology.[60][61] Throughout the occupation of Urithiru, the Sibling revealed that they have several nodes to protect them from enemy invasion.[8] Their last Bondsmith wanted to install several more but was only able to install four nodes across the first few levels of the tower.[10] The Sibling was hesitant to tell Navani the location of the nodes, and only gave them up when Navani convinced them it was vital to protect them from further corruption.[39][10] However, the Sibling's fears were not unwarranted; after the reveal of the third node, Raboniel revealed that she had been listening in the entire time Navani and the Sibling were communicating.[23] The Sibling then refused to talk to anyone until their final node was in danger, when they called on Kaladin for help to protect them from full corruption.[26] While Kaladin fought against the Fused, Navani attempted to push the Sibling towards bonding Rlain, as suggested by Kaladin and Navani. However, there was not enough time to find Rlain, so Navani suggested herself.[4] While hesitant initially, the Sibling accepted the bond, and working together they were able to expel the Voidlight corrupting the Sibling and restore Urithiru to full power.[4][6] When the Sibling bonded Navani, they were finally able to create Towerlight after being unable to hear Honor's tone, or by extension that of Towerlight, since his death.[4]


  1. a b c d e f g h i j Rhythm of War chapter 42#
  2. a b c d Oathbringer chapter 111#
  3. a b Rhythm of War chapter 3#
  4. a b c d e f g h Rhythm of War chapter 110#
  5. a b c Rhythm of War chapter 116#
  6. a b c d e f g h i Rhythm of War chapter 111#
  7. Skyward Pre-Release AMA
    Arcanum - 2018-11-03#
  8. a b c d e f g h i j k l m n o Rhythm of War chapter 49#
  9. Rhythm of War chapter 22#
  10. a b c d e f g h i j Rhythm of War chapter 69#
  11. Surgebinding Chart
  12. Oathbringer chapter 28#
  13. Oathbringer chapter 65#
  14. Oathbringer chapter 59#
  15. Rhythm of War chapter 87#
  16. Oathbringer chapter 42#
  17. a b Oathbringer chapter 64#
  18. Rhythm of War chapter 112#
  19. Rhythm of War chapter 113#
  20. a b c d e f g h i j Rhythm of War chapter 39#
  21. a b c Rhythm of War chapter 55#
  22. a b c d Rhythm of War chapter 70#
  23. a b Rhythm of War chapter 72#
  24. a b c d e f g Rhythm of War chapter 40#
  25. Rhythm of War chapter 89#
  26. a b Rhythm of War chapter 100#
  27. a b c Rhythm of War chapter 56#
  28. a b Rhythm of War chapter 58#
  29. a b c Rhythm of War chapter 37#
  30. a b c d Oathbringer chapter 68 epigraph#
  31. a b c d e f Oathbringer chapter 69 epigraph#
  32. Oathbringer chapter 53#
  33. Oathbringer chapter 28 epigraph#
  34. Oathbringer chapter 8#
  35. Rhythm of War chapter 44#
  36. a b c d Rhythm of War chapter 38#
  37. Oathbringer chapter 30#
  38. a b c d Rhythm of War chapter 105#
  39. a b c d e f Rhythm of War chapter 61#
  40. a b c Rhythm of War chapter 59#
  41. Rhythm of War chapter 92#
  42. a b Rhythm of War chapter 41#
  43. a b c d Rhythm of War chapter 14#
  44. Rhythm of War chapter 50#
  45. a b c Rhythm of War chapter 71#
  46. a b Rhythm of War chapter 101#
  47. General Reddit 2020
    Arcanum - 2020-11-30#
  48. Rhythm of War chapter 43#
  49. a b Rhythm of War chapter 109#
  50. Rhythm of War chapter 102#
  51. Rhythm of War chapter 104#
  52. Rhythm of War interlude I-5#
  53. Rhythm of War chapter 85#
  54. Rhythm of War chapter 91#
  55. Rhythm of War chapter 53#
  56. Oathbringer chapter 67 epigraph#
  57. Oathbringer chapter 65 epigraph#
  58. Oathbringer chapter 72 epigraph#
  59. Oathbringer chapter 70 epigraph#
  60. a b Rhythm of War chapter 9#
  61. Rhythm of War chapter 28#
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