As major of the comments have misunderstood this chapter let me explain it, though major spoilers.soso
Spoiler!
So sung jin woo isnt the old shadow monarch, the shadow monarch we saw is the old monarch, ashborne. Sung jin woo was supposed to be a vessel for ashborne but ashborne didn't want to come back, so ashborne gave sung jin woo his purple heart and thats where sung jin woo became the shadow monarch and the system itself
