The Ancient Relic is a key quest item used in the Saber puzzle, required to progress toward unlocking Saber. It has no combat or gameplay use on its own and exists purely as a progression requirement. Players must collect it alongside the Cup and the Torch, with all three items needed to complete the puzzle chain and move forward in the Saber quest.
Obtainment:

To obtain it, players must first give the Sick Man a filled Cup. After that, the item becomes available through the Rich Man. The player needs to accept his quest, travel to Jean Luc Island, and defeat the Mob Leader. Once the target is eliminated, the Rich Man rewards the Ancient Relic, allowing progress toward completing the Saber puzzle chain.
Uses:
The Ancient Relic is used to unlock the Saber Expert boss room. It is required to open a sealed doorway leading to the fight and has no purpose outside this interaction. At the location near the Blox Fruit Gacha NPC, the relic is placed on a stone platform with a carved slot beside the stairs. Interacting with this slot lets the player insert the Ancient Relic, which triggers the door to permanently open. Once activated, the path to the Saber Expert remains accessible for future visits without needing to repeat the process.