While packing up the props she had recently used for a magic show that did not go as she had originally planned, Trixie Lullamoon encounters a boy around her age who seems rather odd and mysterious, even though he looks like an ordinary high school student like she is.
Not only is he carrying his pet cat inside his duffel bag wherever he goes, but he is also able to have an actual conversation with this cat, despite not having a magical geode like the one that Fluttershy uses to talk to her animal friends.
While she initially sees this man as the key to learning how to do real magic, he ends up helping her in a completely different way.
Ren Amamiya/Joker and Morgana/Mona are both characters from Persona 5, a role-playing video game developed by P-Studio and published by Atlus, which is a subsidiary of Sega.
In terms of Equestria Girls continuity, the story is set right after the animated short, Street Magic with Trixie.
In terms of Persona continuity, it takes place approximately six months after the events of Persona 5 Royal.