Exactly one week after a person turns 15, the possibility of clue marks manifesting increases. A clue mark is a mark that links a person to their soulmate and they only appear when both people are at least 15. First one: age difference Second one: gender Third one: a single interest Fourth one: defining trait (physical) Fifth one: eye color Sixth one: hair color Then from there, the person's initials will appear if the two haven't found each other. In some rare cases, a song can be heard in the heads of both people involved to help bring them together. Most believe this isn't true given how rare it is. Enter Edd, receiving his first clue mark one week after his 15th birthday. And Kevin getting his first the same day at the age of sixteen. ((Nat is C2ndy2c1d's character Nathan "Nat" Goldberg. I don't take credit for this character))