JD, who described himself as an "amazing brewmaster," was in charge of the Sunday Brothers' alcohol and moonshine distillery operations. He respected Abigayle Singh. Even though the brothers lived quite well and had supplies in their situation, JD was very depressed by the post-apocalyptic world they lived in, but met his ex-girlfriend named Brianna Hawke at Harpers Ferry. JD and Brianna had dated before the Great War. She eventually became his girlfriend again and his mood cheered up, although he began to emotionally distance himself from his brother.
After an attack on Harpers Ferry, Brianna showed up at the brothers' cabin with a small group of survivors. Jesus claimed Brianna had conned JD, pretending to love him in order give herself and her friends an invite to their bunker. Brianna Hawke's diary supports this, saying she felt the two brothers had snobbish attitudes and reveals she and her group had been stealing from the brothers' land, having raided the food in their field. However, it is ambiguous if she truly fell in love with JD and if her opinion of him changed when he began giving her supplies.
Jesus declined Brianna's invite, opposing JD. Jesus then knocked JD unconscious and fired warning shots to scare Brianna's group away. Weeks later, Jesus thought JD had let go of Brianna, but it turned out they were secretly exchanging notes and that JD had been giving her supplies.
Jesus tried to confront JD about how Brianna was a bad influence. A physical altercation happened between the brothers, and Jesus accidentally killed JD by shoving him off a cliff, unsure if JD slipped or if he pushed too hard. Brianna found out what happened and Jesus and Brianna's group ended up killing each other.
Juan Diego "JD" Sunday is mentioned only in Fallout 76.