Tyriyn Bythronian
Tyriyn Bythronian of Ubl is the High Priestess of the Temple of Lorminstra in Wehnimer's Landing. She is the very old black robed woman who performs the ritual for offering sacrifices in exchange for deeds. She refers to herself as a "Daughter of the Night, High Priestess and faithful servant to the Lords of the Great Moon." This messaging dates back to the early I.C.E. Age when it was the temple of Eissa in Kelfour's Landing. The deed ceremony is not based on the Shadow World source materials. It was unique to GemStone's death mechanics, which included Purgatory and the risk of permanent death.
Her name is known to have been "Tyriyn" since August 1992 at the latest, and was probably the same all the way back through early 1990 or late 1989. This would most likely pre-date the Sisters of Eissa religion, which is first mentioned on page 50 of the Shadow World Master Atlas Addendum from later 1990. Her epithet "Daughter of the Night" is presumably rooted in Eissa and Reann being "siblings."
I.C.E. Age
The "Great Moon" is a term for the moon Orhan (Modern: Liabo) on page 17 of the Shadow World Master Atlas from 1989. The "Daughter of the Night" title, however, does not come from a source book. The placename "Ubl" does not have an obvious Shadow World original, and does not appear on any De-ICE conversion list. Ubl may have been part of the original wording, where it would not be copyrighted.
Sisters of Eissa
The Sisters of Eissa are always female and mostly women of mortal human races. They are typically healers or clerics and the priestesses who can perform resurrection magic. They abhor killing except in self-defense, even things such as orcs and goblins, and are strict vegetarians because they believe animals have souls. They are healers who only ask for donations proportional to what has been exchanged. The chief priestess of a temple is called the "eldest", followed by the "elder sisters", and the "sisters", and finally the novitiates. They wear flowing white gowns but put on hooded black cloaks when outside the church. Their ranks are correspondingly a gold belt with crystal keys, silver belts, blue belts, and white belts. This is relevant because these features are not seen in the Landing temple or Tyriyn Bythronian.
In the Shadow World Master Atlas, 2nd Edition (1992) they were slightly elaborated to have temples in most cities, and they are punished with having their powers cut off if they travel with a group that kills. This is when the six keys to the Gates of Oblivion are defined: Life, Death, Mind, Body, Soul, and the Void. In the first edition Life and Death open the Gates, while the Void is never used, but the other three are not mentioned. In later books they believe souls who have not earned the afterlife will return to the world in some form of reincarnation. They do not have congregations and coexist with other faiths.
Inconsistency:
The hooded figure at the tapestry, however, is described as being a man. The Lord High Cleric is probably the old priest who explains the deed ritual the first time it is attempted by an adventurer. Thus, the GemStone implementation of the temple of Eissa seems inconsistent with the Eissa religion of Shadow World, but this is easily understood as being slightly older than the documentation. The Lord High Cleric's office notably refers to the "Lords of Liabo and their Sages", which probably read "Lords of Orhan and their Loremasters". This is an unusual combination that would most likely be rooted in the brief history sections of the 1989 adventure modules which speak of the Loremasters as perhaps descendants of the Lords. Research:The Graveyard argues this is probably in parallel with The Graveyard.
The premise that they believe in reincarnation for those who have not yet earned the afterlife is seductive, but it was not in the Shadow World books until after GemStone III was no longer licensed for that world setting. These later Shadow World texts, such as Powers of Light and Darkness (2003), also specify that there are various afterlives beyond the Gate of Oblivion. When GemStone III was set in Shadow World the other side of the Gates of Oblivion was still undefined, other than being another plane. Later books also have the River of Life including flows of essence bringing souls to the Gates of Oblivion.
Deed Ritual
The premise of the deed ritual is that sacrifices are "gifts" being given to the High Priestess as a high tithe for her intercession, but that she has substantial influence with the death goddess, who the acolytes (like Bandur Etrevion) refer to as Death. It is explained that the goddess has no use for "the trinkets and baubles of this world", but she acknowledges we value them, so we must "offer proof that your life is worth more to you than the treasures you possess." The High Priestess prays on your behalf, but warns "the proof must be overwhelming" to the mind of Death. They are recorded in a Book of Passing. (Eissa does not allow the return to life of those who have died in significant or meaningful ways, but she will make exceptions for those who died before their time or who have incomplete missions in the world.)
The goddess herself decides whether this sacrifice is convincing by either making the room cold or the incense burners bursting in brilliant blue flames. There is maybe a dark parallel to this in the tapestries and incense burners in the Sheruvian summoning chamber, where this ritual is also symbolically represented in the Dark Shrine of the Broken Lands and the purgatory throne room of The Graveyard. It might also be argued that the High Taskmaster who directs sacrificed spoils, which are offered on an altar, is the Council of Light analog to the High Priestess with Grand Poohbah analogous to the Lord High Cleric.
Messaging Variants:
The ritual itself is considered a puzzle, though the steps are explained. These same steps are in Kelfour Edition newsletters from 1990. The following are messaging variants upon entering the tapestry:
As you approach the black velvet tapestry, the hooded figure stands and steps in front of you. In a quiet but firm voice the hooded figure says, "I cannot recall thy face, XXXXX. Either this is thy first visit or thy features have become twisted to my eyes by the touch of Death's hand. But it matters not. This is the Temple of Lorminstra and you are welcome. Acolytes are waiting to assist you on the other side of this curtain. May you find the answers that you seek." As you approach the black velvet tapestry, the hooded figure stands and steps in front of you. In a quiet but firm voice the hooded figure says, "To the Gods, the life of this world is no more than the flicker of a candle. You may enter, XXXXX." As you approach the black velvet tapestry, the hooded figure stands and steps in front of you. In a quiet but firm voice the hooded figure says, "The quest for life eternal is common in these lands, XXXXX. May our Gods find favor with thee." As you approach the black velvet tapestry, the hooded figure stands and steps in front of you. In a quiet but firm voice the hooded figure says, "One must admire your lust for life, dear sir. Enter XXXXX, and may Lorminstra shine favor on you." As you approach the black velvet tapestry, the hooded figure stands and steps in front of you. In a quiet but firm voice the hooded figure says, "May Lorminstra grant you even more deeds, XXXXX." As you approach the black velvet tapestry, the hooded figure stands and steps in front of you. In a quiet but firm voice the hooded figure says, "I see that death has yet to make a final claim to thy soul, XXXXX. Welcome back."
Behind the Scenes
"Tyryn byth ronion" is Welsh and the spelling "tyriyn" has existed historically. Ubl is probably not Welsh and might be medieval German. Tyriyn might also be interpreted as "tirion", which is also Welsh but a different meaning, or a variant spelling of "tír eoghain" which is Irish. These possibilities are worked through in Research:The Graveyard, which speculates about the meaning of the deed ceremony. Ubl was retconned to be in the southern Turamzzyrian Empire. Deeds only exist now to reduce the severity of Death's Sting. They have no role in whether souls are brought back, in spite of the archaic messaging.