The Yama Underworld did indeed lack a Leader on the level of the Queen Mother of the Western Heaven.
Its upper echelons were composed of the Ten Hall Yama, corresponding to the Nine Great True Immortals of the Celestial Court. The three strongest among the Ten Hall Yama jointly controlled the Yama Underworld. However, these three strongest King Yans refused to submit to one another, and all harbored ambitions to become the sole Leader. This essentially kept the entire Underworld in a perpetual state of infighting.
Fortunately, their all-out war against the Pinnacle Celestial Immortal Sect temporarily diverted their internal conflicts. Otherwise, the situation in the Yama Underworld would undoubtedly be even more chaotic.
