Red Ligaments

The moment an ajin dies, both them and their soulmate have a thin red string appear around their wrists, varying in style, design, shade, thickness, and transparency. People with red strings are pretty heavily discriminated against, since that means either they are an ajin, or their partner is an ajin.

At the same time, you want to be aware of your wrist if you don't have a line. If you go to sleep and wake up with a red line, for example, you have no idea if you're an ajin who died abruptly in your sleep, or if your soulmate died somewhere else.

Just to make matters worse, soulmates can't stay away from each other once they've met. Once a pair has met, most would want to be with their significant other. As time goes on, your crave for their touch becomes top priority. The longer you're away from your known soulmate, the more the link will force you together.

When a girl hates her soulmate and wants absolutely nothing to do with him, it's a challenge to keep herself away as the link becomes unbearable and just being in the same building as him makes her legs quiver with need and want.