Airships

Airships are a type of large-scale aircraft used for travel.

Description
Marulk's father used an airship to travel to and into The Abyss, which resulted in a fatal crash that cost him and his crew their lives. Marulk was the lone survivor of the incident.

A scene depicting the discovery of The Abyss (shown in Chapter 1) indicates that primitive airships may have been in use as far back as 1,900 years prior to Riko's journey.