Yethlūl s.yen'o (Yā'mon III) is the third planet from the sun of the Yā'mon system, Xi'an Empire. Along with the nearby planet Yethlūl y.ath'o (Yā'mon II), it is being jointly terraformed by the Human corporation ArcCorp and the Xi'an government. This long-term collaboration is expected to benefit both sides as they share their technologies and methods with one another. In 2948, the planet was flooded with a violet-hued gas as a step in the atmospheric construction process. Part of the Koa e Ko'ia endurance race took place on Yethlūl s.yen'o in 2947.