Several rare materials in Octopath Traveler 2 are needed for players to level up members of their party or upgrade pieces of gear, and Ancient Sentinel Cores are one of the most elusive items to find with only a couple known locations in the world. Although players are capable of finding these Cores as random drops from enemies or in regions around Solistia, the rarity of these objects makes them difficult to find this way. By following the story chapters of a specific character, players are able to find Ancient Sentinel Cores in a reliable spot rather than grinding for the material through tedious fights.

https://screenrant.com/octopath-traveler-2-ancient-sentinel-cores-locations/