Total Recommendations: 2
A seemingly ordinary boy is enamored by a special girl that he meets in a fated encounter. Together, the two embark on a journey around the world aboard a magnificent and powerful vessel, doing battle with an evil army. As the adults nurture them and the children look up to them, the girl undergoes changes as the boy makes her experience feelings she has never had before, and the love between the two develops and strengthens. When the truth about the girl is revealed, the boy must face his obstacles with courage.
Both series have similar world-building in that the protagonists find relics of an ancient civilization on Earth and the origin of humanity are similar in both series.