Death's Sympathy was a technique that Rui had stopped using because it didn't work against Martial Artists of the Upper Realms. The powerful technique had served Rui extremely well in the Senior Realm, but Martial Artists of the Upper Realms had too much control, efficiency, and mastery of higher principles in their movements.
However, the same was not necessarily true for other pathwalkers. Efficiency and control were not parameters that they even considered. Instead, they simply consumed more energy than Martial Artists, requiring enormous supplies of energy just to sustain a single battle. Rui couldn't even imagine how much energy it took to sustain the Dragon Emperor directly or indirectly. Even the energy that they drained from the Sun with their Dyson Spheres was likely not enough to fully quench their great thirst for energy.
