Aoi Umi no Tristia

Tristia was once a thriving ocean city central to maritime trade, known for its beauty and referred to as "marine jewelry." Over time, a dragon attack caused its decline, and despite the people's efforts to rebuild, the city worsened. In their final attempt to restore it, they turned to Prospero Flanka, a renowned inventor who had saved other cities from ruin. When Prospero finally arrived, only one person greeted him at the port. He had sent his granddaughter, Nanoka, in his place.