Fallout 4's Har Harbor DLC has plenty of content for players to absorb, including tensions between several key factions on the island. One of the central factions is the religious cult known as the Children of Atom, the arch-rivals of the residents of Far Harbor itself. Players can opt to join the Children of Atom, and will likely need admittance into their base, The Nucleus, in order to complete many of the main story missions in the Far Harbor DLC.