Castiel corrects the idea that the Antichrist is the son of Lucifer. The Bible, according to Castiel gets more wrong than right, and the Antichrist is not the son of Lucifer, but demon spawn born of humans. They are also known as cambion. This lineage makes them incredibly powerful; the Antichrist can teleport anywhere instantaneously with a single thought. They can create minor tremors just by clenching their fists. The Antichrist gains more power while Lucifer is on Earth.
After investigating Jesse Turner's history and finding demonic involvement, Dean and Sam Winchester call Castiel for help. Castiel explains to them that the chaos Jesse has been causing is nothing compared to what it could be if he were to get angry. He then reveals that as the Antichrist, Jesse is destined to align with Lucifer and, "with one word, he can destroy the entire Host of Heaven." Refusing to allow such a risk, Castiel resolves himself to kill Jesse, with or without the brothers' consent or help. Before he could be killed, Jesse instinctively transforms the angel into a action-figure-sized version of himself.
In the moments that follow, Dean and Sam arrive and tell Jesse that he is a superhero and they are going to "train him."Julia interrupts while possessed by Jesse's demonic parent; she tells him the brothers are lying and that his whole life has been a lie, which angers him.
Sam admits to lying to Jesse and promises to tell the truth - when Julia tries to stop him, Jesse intervenes by releasing Sam and immobilizing her so he can hear Sam out. Jesse is overwhelmed by the fact he's half-demon but Sam reminds him that he is still half-human and thus can still be good. Jesse promptly exorcises the demon from Julia.
Later, Jesse asks the Winchester what he should do and they tell him it's his choice. He asks to bring his parents with him and they tell him he can but it would put them in danger because both angels and demons will be trying to find him. He says he's going to say goodbye to his parents but instead writes them a letter and vanishes.