Board Thread:Questions and Answers/@comment-4929778-20160415205315/@comment-37493549-20190117170100

Don't you think it's more logical that for a happy ending, they would get rid of the power of the titans by somehow 'giving it back' to wherever it came from? Perhaps by someone collecting all 9 titans and then allowing the devil to eat them. Or the devil eating them individually, but that's a bit less dramatic.

Maybe that was actually the original deal Ymir made with the devil now that I think about it. Maybe she was supposed to give the power of the titans back, but refused and was cursed with the 13 year thing as punishment.