One must die to have the other twin live

"Can't we all just live together?" It would be nice, but for the twin brothers Il-do and Yi-do, it's just a wishful thought. Born under a cursed fate due to their parents' original sin, one must die for the other to live. To avoid this, they have deliberately cut off contact. However, when Yi-do, who works for a gang, gets stabbed, Il-do somehow hears about it and rushes to donate blood, saving his brother's life. But instead of gratitude, Yi-do attacks him the moment he sees him.