Naturally, as the years passed, he did not remain stagnant in strength.
Using his self-created technique, the Divine Body Technique, his advancement has been constant and uninterrupted.
But since he needed to advance all three of his body, mind, and soul together, it would require more energy and dedication.
Even so, he managed to reach the peak realm of mortals, at a level that any genius of his generation would have just reached.
They would naturally achieve it in the final stages of the mortal realms.
Zelo was also one step away from entering the last stage of the mortal realm, he was about to enter Nirvana.
Due to his harsh advancement requirements, he fell behind geniuses like his sister Vivian who had already entered Nirvana and was about to enter its middle stage.
But that was only in terms of energy, because in terms of fighting ability and mastery of techniques and such, he could easily beat an immortal solo.
