What's Wrong With Taking Advantage of Others in the Bizarre World?

There exists a strange staircase. At the stroke of midnight, it transforms from having 12 steps to 13 steps. Anyone who steps onto this cursed staircase encounters terrifying supernatural events and disappears forever.
If you found yourself on this staircase, what would you do?
Simple—just use a “Buy 12, Get 1 Off” promotional coupon to make the extra step disappear! Problem solved~

Original Webtoon