Blood String and Faith

There is this Japanese belief that the gods ties a red string on a persons pinky finger. This red string help lead people to the ones they are destined with.

They say, that no matter how far or how vast the distance is between those people connected by the red string, they will eventually find each other, even if it isn't during their lifetime but on the next.

However, what will happen when the string become tainted with blood? What fate awaits the destined?