Kai Booker is a barista at Goblins, a coffee shop Erica frequents. In the Season 2 premiere, Erica learns that Kai is also a patient, and befriends him.

Kai Booker is a rock star from the year 2019. He is sent back to 2009 to finish a song called "Alien Like You". However, unlike Erica, he has spent months in the past, trying to change the past, improve them somehow, and reluctant to finish his song so that he can return to his own present. His Therapist is Dr. Fred, who has called on Erica's help with Kai on various occasions. Kai and Erica share an attraction, and although Erica tries to fight it, due to her being in a relationship with Ethan already, she later comes to terms with it. At the end of Season 2, Kai finishes his song but is still stuck in his past. He calls on Erica to help him finish this session. He performs Alien Like You in Goblins to a record producer who liked his boldness to play his own song. When Erica comes up to congratulate him on his song, he doesn't remember her at all. He quits his job the next day.