He began the breakthrough with ease. His soul wasn't pulled taut as others do theirs. It expanded on its own and superimposed itself on his body. He is his soul more than he is his body. There's no need to force his soul to behave. It is his body that will give him trouble, not his soul.
His soul didn't experience any pain or discomfort from leaving the soul realm. His soul could already exist in the physical world as a Sovereign when he separated it painfully from his high elf body. So this isn't a problem at all.
He was about to begin the fusion of the physical body and spiritual soul, two of the aspects of his existence, to achieve transcendence when the Stigmata on his back activated. It shone brightly like never before and began pumping divine power into Helios's body. It was like a river of divine power started to pour out from it instead of the trickle that ought to come out of it.