He crouches in front of Jack and pulls him to his feet, kindly saying that his family -- Dean and Cas -- helped him through his troubles and now he wants to help Jack. Prior to the Team Free Will's arrival to the Apocalypse World, Jack and Mary lead several attacks at many bases located in the Great Barren Plains, containing garrisons for each one. Time to time by Jewels, Jack's hairstyle is reference to looking similar to that of Leonardo DiCaprio until Post-Season 14 when he cuts his hair and keep sit comb.

During this time, Jack played a role in the resurrection of Castiel who he had chosen as his father. Finally, with a scream from Kaia, the two emit a yellow glow that opens a rift and sends out a wave of energy that Due to Kaia flashing between Mary and the Bad Place, the group ends up separated from each other. Reaching the church indicated by Ruby, Jack notes that it all seems too easy before they are ambushed by two After returning to the bunker and sending their alternate selves away, the Winchesters are told by Castiel that Jack has changed and he is the first being to visit the Garden of Eden since the exile of humanity. With Jack saved, and armed with the location of Jack is sitting alone in the Bunker kitchen eating a bowl of cereal when Castiel finds him. Jack assures them that they'll be fine and he is in control, but an afraid Stacy accidentally runs into the path of the flying blade, critically injuring her. Sam tells Jack that just like Kelly and Castiel did, he has faith in him.

All members of Team Free Will head out together to deal a case, only to end up with negative results as Jack accidentally kills a man, causing him to be afraid of having anyone around him as he fears he might hurt them so he runs away, concealing himself from everyone after him. Despite being somewhat disappointed he didn't meet another Nephilim, Jack was curious about the female Nephalem and was interested to learn her goals, along with her group were interested in bringing Michael down. Angry, Jack begins tapping into his powers, causing the box to shake and eventually explode, causing alarms to go off in the Bunker. Kaia puts on some of Jack's clothes and leaves with Jody, eager to see Claire again. Jack's sense of being useless also became more significant when he struggled with trying to adapt to fight like a human until his powers return and felt completely useless when he failed in adjusting to it and was unable to help in the mission to save Castiel, which led him overpowered by the demons holding Castiel prisoner. They decide to forgo the training for the time being. These are the cast members of the fifteenth season of Supernatural: Jared Padalecki as Sam Winchester, Jensen Ackles as Dean Winchester, Misha Collins as Castiel, Alexander Calvert as Jack Kline / Belphegor, Jim Beaver as Bobby Singer, DJ Qualls as Garth Fitzgerald IV, etc. In the confrontation that follows, Noah proves to be more than a match for both Jack and Castiel, infecting Castiel with his poison and knocking Dean out when the Winchesters try to intervene. Sam, Dean, and Cas arrive soon after to find Jack choking the young man. He proclaims his intention of destroying that life by having her kill the hostages but she refuses and tells him to kill her. The Winchesters arrive on time to stop the process and after learning he was tricked and his friends are being hurt by the Prince, Jack scares Asmodeus into fleeing. Sam eventually finds Jack sitting in an alley and comforts him by explaining that Dean’s aggressive behavior is the way his fear manifests itself, and that Dean is just looking to protect Jack, as well as other people from Jack due to his powers.

She threatens to tell Billie if he uses his powers again, but Jack dares her to go and says he'll use his powers anyway. Revealing his Nephilim nature, and showing how he differentiates from typical Nephilims due to being the son of an Archangel, Jack's eyes glow golden and his wingspan are about the equivalent size of those from an Archangel. While a fight with Team Free Will and Lucifer is engaged, Jack is given birth, at the same time with his mom dying. Dean attempts to comfort Jack, telling him he has nightmares of the people he couldn't save, too. As Castiel steals Dumah away into the hall, Jack hears a prayer from Sam inviting him back home.