Help me!

Hi! While I was downloading manga (to read it offline)... I remembered a manga and I read it somewhere not here and the plot was the twin died and there was a pocketwatch and [I can't explain it] and the other twin will continue what was the other twin didn't do. It was like a game. And the character that I remembered was 'Cain' [It's not the real name of the MC because he made this name up]. Help me find this manga. It is korean, I think.