Martial Master; it was a stage beyond a Harmoniser. But in actuality, Martial Masters were in essence, still Harmonisers. Based on her understanding from what Mu'Tua had informed her vaguely, Martial Masters only differed from Harmonisers in one regard: They were able to use their race's Racial Qi—Kalki Qi.
And it seemed to become a Martial Master, one needed to achieve certain conditions first. And upon obtaining the qualifications, they would receive an invitation to meet with their race's Fourth Celestial Emperor and become Martial Masters.
Mu'Tua did say that there were cases where one became Martial Masters naturally. But those were incredibly rare. Most were turned into Martial Masters by the Fourth Celestial Emperor. But, when she inquired further about it, Mu'Tua remained tight-lipped.
Rather, it seemed as if even she herself was unsure about the details, despite being close to reaching the peak as a Harmoniser.