If Jack (Milo Ventimiglia) and Rebecca's (Mandy Moore) relationship on This Is Us didn't give you serious couple envy, we might not be watching the same show. The Pearson parents may not be perfect — their petty-as-hell fight over Rebecca choosing to go on tour with her ex-boyfriend Ben (Sam Trammell) proves that — but their love story is one for the ages. No TV couple seems better suited than Jack and Rebecca — and every couple deserves their own song. Now, a new fan theory thinks that they've cracked the code on what song will be special to this couple — and it's got the same name as the This Is Us finale.