Good, now that the spoilers tag is working again, I can ask my question:
Isn't it rather too lucky a coincidence that Eruru's ring is really the master key to Hakuoro's "birthplace"? Given that it appears so ordinary, I very much doubt that anyone would have realized its significance and passed it down for the many generations required to reach Utawarerumono's time. It would have made an interesting sub-quest to find the key in the game.