[kbenson]

This point is driven home by Justin’s insatiable desire to uncover the mystery of his Spirit Stone, and the ancient Angelou civilization.

My mind immediately jumped to the idea that this is a play on words for the ancient Maya civilizations, and Maya Angelou. Apparently I wasn't the only one.[1]

1: https://gamefaqs.gamespot.com/boards/197483-grandia/53620555