Opening the True Spirit Gate was not a "real" action as much as it was a concept.
According to everything Liora knew, a Devil's True Spirit was sealed within the gate, unable to escape its cage.
To unleash it, one had to open the gate. Hence, this stage came to be.
This process didn't require physical strength, but instead required the Devil's soul to carry a certain "weight".
Their overall strength, their insights over their journey, the techniques they had practiced, and even the bloodline itself all factored in that "weight".
For most Greater Devils, opening the True Spirit Gate was a process of long-term accumulation.
They would have to spend thousands of years slowly pushing it open before they could free their True Spirit sealed inside.
Of course, this was the case for the most talented Devils.
Most people would never reach this stage, while the majority of the few who did would remain stuck in it forever.
