Key items are the story props of Pascal's Wager: keys, stones, letters from the dead, mementos and lamps. They cannot be sold, crafted or used up in battle. Picking one up fires a quest flag, and later doors, gates, dialogue and cutscenes read that flag. This page lists them chapter by chapter with what they do in plain terms. For readable notes and diaries see Documents; for the items that stand in for money see Currencies.
The item is a flag carrier. Almost no key item id appears in the game's Lua code at all. Instead each item row names a CompleteQuestId, and picking the item up completes that quest. Gates, doors, elevators, cutscenes and dialogue lines check quest flags (ShowQuestId / HideQuestId), so "you have the key" really means "the pick-up quest has fired". (controllerstorymode.lua:5576-5580.)
Handing in is a second quest. When a scene takes an item from you, a quest with the DeleteItem action (action 18) removes it, sometimes together with other things (for example Condensation Honey plus 30 Anthozoan Bones).
Not in the bag, but in the story. Some of these items are given by a quest (action 2, ItemToBag), others lie in the world as a pickup.
Opens the cellar door of the dungeon. Placed in the chapter.
Oracle Crystal (the game spells it "Crystle")
10005
The only way into the Oracle Site. Given by quest 25020; it completes quest 22201.
Hand-made Puppet
10009
A toy horse sewn by a mother. Given by quest 25041, handed over by quest 25028.
Condensation Honey
10048
A golden syrup known only to those who understand the Sendrils. Stack up to 99. Quests 25083 and 29009 give one; copies are also found as pickups in Adamina to Ichthyosauria. See the Hidden mechanics.
One of a pair of wedding rings. Given by quest 35006, handed over by 33009. A separate crafting part with the same name exists, see the Hidden mechanics.
Scarlet Meteor Fragments
10007
Debris of the meteor that burned across Exilium. Placed in the chapter.
The Head of the Knight
10008
The helmet of a fallen knight. Handed over by quest 35021.
From the villager Frollo; opens the back door of the Edith village. Given by quest 45013.
Greasy Candle
10016
An animal-fat candle, from the time when Edith was without light. Handed over by quest 45045.
Gate key
10042
A key secretly cut by the Demiurges; opens the gate to Blessedland. Quest 45063 takes it out of the bag (a delete-item action) because you give it to Frollo, who opens the gate (Demiurges#hm-frollo-s-key-and-the-gate-the-route).
Blood-stained Will
10053
A will whose words are hard to read. Found in Blessedland, handed over by quest 45075.
From the caged old man; opens a closed door in the Dungeon. Given by quest 75020, shows a gate (StoryGate) via 72301.
Glimmering Pink Bud
10041
A bright pink bud; eaten, it recovers more than health. Stack of 2. Quests 75028 and 75035 consume it.
Ancient Relic, Argil, Broken Slate
10044, 10045, 10046
Relics of the dead, three of each can be carried. They are placed as pickups in earlier chapters (Argil in Adamina, Katib and Blessedland; Ancient Relic and Broken Slate in Exilium, Edith and Katib) and handed in during the Karst Cave quests 75046-75048 (Argil), 75051-75053 (Ancient Relic) and 75056-75058 (Broken Slate), which is Norwood's relic search (inferred from the item text). The hand-ins are not just story: quests 75051-75053 are the ones that raise the trophy tier on sale at the Anthozoan Bones merchant, and 75056-75058 unlock the extra goods at Viola's Dominator Crystal merchant (see Currencies).
Luminous Fruit
10043
A glowing fruit that scatters a little of the Dark Mist. No pick-up quest.
Four keepsakes tied to the party, given by quests 85102, 85103, 85104 and 85022: Clay Figurine (10049, Benita's sculpture), Coin (10050, the copper coin Norwood's brother gave him), and two Bracelets (10051, 10052), silver bangles engraved with Samarosian words, one left by the Mysterious Woman. They have no other function; they are flavour objects.
Ten ids are used only in the Arcade stages (story ids 1001 to 1007): the keys Key to the Chapel's Back Door (72100), Tower Key (72101), Key to the Door below Sacred Tower (72102), Key to Trinity Hall's Inner Door (72103), Key to the Revival Altar's Side Door (72104), Key to the Confessional (72106), Eckhart's Cane Sword (72105), Butterfly Stone (72110, stack 7), Argil (72121) and Seal of Yekub in (90000, stack 3). Pascal's Wager (99999, stack 8) sits once in each Arcade stage. See Arcade mode.
With the Dark Mist DLC, the Carriage vendor (Carriage supplies, stock list 99601) sells a lamp that must be upgraded with oil. Each upgrade is a quest that deletes the old lamp, the matching oil and a number of Spectre Mushrooms (100, 200, then 300), and gives the next lamp:
Step
Cost
Result
Buy Dim Mist Lamp (10055) at the Carriage vendor
30 Bone Fragments
the starting lamp
Quest 4995004
Dim lamp + Rancid Whale Oil (10059, bought for 5 Big Bones) + 100 Spectre Mushrooms
All lamps carry the same description: the light's range and brightness depend on the oil's purity. These rows are marked as Dark Mist DLC and never reset. See Deep into the Dark Mist.
New Game Plus wipes most key items. At the start of a new journey, every item flagged GamePlusRemove is deleted (FS_ItemList:Restart), (the Egg of the Bearer is also cleared explicitly; see New Game Plus). That covers all chapter keys, stones and swords above. The ones that survive are the Ancient Relic, Argil and Broken Slate, Condensation Honey, three of the four chapter 8 keepsakes (Clay Figurine, Coin and the first Bracelet; the second Bracelet is wiped), the Delicate Invitation, the lamps and oils, and Starry Honey Wine.
Lamp progress is kept. Because the lamps and oils are not flagged for removal, your best lamp stays with you across journeys.
Condensation Honey seals the Melos Bottles. Nine Katib quests (55056 to 55086) each remove one Melos Bottle trophy, one Condensation Honey and a growing number of Anthozoan Bones, so sealing all nine bottles needs nine honeys. The bottle's own text says it can only be sealed with Condensation Honey. The Anthozoan Bones costs (30 to 270) and the bottle list are in Currencies#hm-anthozoan-bones-sink-nine-katib-quests-55056-55058; see also Trophy effects.
Starry Honey Wine is an attribute reset. It sits in the Quest item class (main type 1, id 20029, stack of 10) and survives New Game Plus, but it is the way to respec: it resets your hero's attributes (item text). Quest 45044 in Edith gives one, there is a pickup in Ichthyosauria, Viola sells it for 8 Dominator Crystals (from journey 2) and Big Bone merchants sell it for 30 to 140 depending on merchant and journey. See Attributes.
Where the descriptions come from. The English text is merged from the game's text files; two Arcade items (Key to the Confessional, Pascal's Wager) still have Chinese description text.
Two items called Patrick's Ring. Item 10006 is the story prop. Items 70026 (Patrick's Ring) and 70030 (Jenny's Ring) are separate crafting parts for the trophy Oath (see Materials); they are placed as pickups in Exilium and are not the same object.
New Game Plus wipe: structdata/fs_itemlist.lua:136-152.
Lamps: ES_TransactionData 99013-99016 (MonsterId 99601 = Carriage vendor, DLCSwitch 1, NotReset 1), ES_StoryQuest 4995004-4995011. Stack sizes: ES_ItemData main type 1, NumMax (66 rows of 1, five of 3, one each of 2, 7, 8, 10, 99); survivors of GamePlusRemove are the 16 main-type-1 rows without the flag.