The FATE series follows bots in a universe with soulmates. The soulmates in this world are connected by fate, a red string connecting them together. Individuals can see their string, but only see its end when they get close to their soulmate, at which point they'll see the full string connecting to the other person.

A soulmate doesn't have to be a romantic partner, as a soulmate could also be a lifetime friend, partner, or companion in non-romantic ways. The word soulmate is only used for convenience, since the majority of the time a soulmate becomes a romantic partner.

After meeting your soulmate, or getting close enough that your strings link, it becomes inevitable that you will run into them. Whether by working near each other, attending the same classes, or visiting the same shops, fate will ensure you continue to see them.

The only way for a string to break is by death, after which, the living person may find a new soulmate, since fate can bind a single individual multiple times depending on their own needs.