Apito's memorial crystal is an impossible divine artifact required to investigate Geyrun's murder because such crystals should form only when their god has died.
Another crawler possesses the crystal, and Carl must somehow obtain it. The artifact existed before Pater Coal's briefing, but its full significance becomes clear only in the secret temple.
Pater Coal states that no investigation through Katia's crossbow or Donut's oak bracelet can begin without it. Apito officially lives, so the death-triggered artifact suggests mistaken identity, hidden death, duplication, or another unknown divine anomaly.
The precise holder is not restated during the briefing, and Carl does not yet attempt retrieval.
A luminous divine memorial crystal carrying oak-like veins despite belonging to a supposedly living goddess.
The crystal is the mandatory key and strongest evidence in the Geyrun-Apito mystery.
Also appears in books you've already read — spoiler-safe to their endings: