Who he is???
Would be better if you dunno for now cause its one of the plot twists, but if u rly must know, he is.... [spoiler]
...he is Yoo Junghyuk from the 1863rd turn of the original Ways of Survival. Might be confusing, but there are several Yoo Junghyuks out there lol. Theres more explanation but its still faaaar away unfortunately. In the novel its around ch400+ iirc
I still wonder to this day that what if KDJ somehow chose SP as his sponsor considering that [spoiler]
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KDJ is YJH's sponsor who gave him the Regression stigma.
Lmaoo that angry vein on secretive plotter if only you know who he is