The adventurer Adol Christin compiled more than 100 travel journals over the course of his life. This story is adapted from one such journal, the Periplus of the Gaete Sea. In it, Adol found himself on the accursed Isle of Seiren, from which none have ever returned. It was there he built Castaway Village, where he could defend himself and other survivors from giant beasts known as the Ancient Species.
During this adventure, Adol recounts his dreams of a blue-haired girl and the lost civilization from which she comes. Ever the curious one, Adol sets off to uncover the mysteries of the island and the identity of this mystical girl.