In the Percy Jackson universe, soulmates exist and everyone has one or two. Everyone is born with one or two. You only discover who your soulmate is by touching skin to skin and then a soul-mark will appear somewhere on your body. Before that, you won’t feel or sense them at all. Totally not knowing who your soulmate could be, even the gods can’t who it is before touching skin to skin. When touching, the mark forms, lights up and the bond immediately clicks in place.