- Full Name: Ayerton Grenavan (Ayrton Glenarvan?) (エアトン・グレナバン Eaton Gurenaban )
- Species: Human
- Born: November 15, 1860
- Origin: London, United Kingdom
Ayerton is first seen in the series as a scientific officer aboard US warship Abraham; he states he's been sent on a secret mission to investigate the sea monsters phenomena. Later in the series, Jean and Nadia meet him again partially buried on a mysterious moving island, completely drunk and telling stories about a strange witch who inhabits the island (who naturally turns out to be Grandis). While on the island, Ayerton falls in love with Grandis, and to strike her, he pretends to be an English nobleman who's going to inherit a large wealth from his family.
Ayerton is quite a weird, loudmouthed character, who is never really able to completely grasp the reality around him, and to tell good from evil. In the epilogue, Marie says that Ayerton was really a noble and wealthy man, and eventually he returned to his homeland.