The first step in sealing Hell's willpower in his left arm was to first weaken it enough, which meant draining its remaining energy to the point only its consciousness remained.
For him to do that meant he had to attack his left arm and shake the energy that remained in the body of light.
Yun Jhin took a look at his left arm apathetically before he used his right fist to punch it over and over again... it was a pretty simple way, just shake the arm good enough so Hell's willpower could 'barf' up all of the energy it had.
"Hey hey... Yun Jhin, come on? Aren't we birds of the same feather? Please let me out! I can promise you I will never bother with you again and I will also give you some more benefits!"
Yun Jhin snorted, now that this thing was sealed into his left arm it became as docile as a lamb, but that was only because it couldn't go towards the brain of his body so it could vie for supremacy with him again.
