On the Saint Seiya side, the search results show that "exclusive" merchandise is quite common. One result details a "Funko POP! Animation: Saint Seiya - Sagittarius Seiya Gold (Alliance Entertainment Exclusive)," proving that limited-run collectibles exist for this franchise. As such, an "exclusive stone" could be a physical collectible item, such as a replica gem, sold as a special edition bonus for a Sasha-related figure or Blu-ray set.
If you’d like, I can:
: The exclusive version often includes additional character skins, early-game power-ups, and hidden lore documents that expand on the history of the Scarlet Demons. Mastering the Scarlet Demons Stone eng saint sasha and the scarlet demons stone exclusive