Ginji Sasaki once belonged to a one-hit wonder band, but has since dropped out of the celebrity radar and tried to eke out a living as a record producer. He earned a reputation of making advances to the women he represents, teenage idols in particular. In desperation, he performed the Master Joker summoning ritual, and was enlisted by Joker into the Masked Circle as one of the Masked Four, Prince Taurus, tasked with collecting Ideal Energy from young people. Through rumors he spread, he created a fake band called MUSES, involving Lisa Silverman, Asatchi and Miipo from Seven Sisters High School. However, he is humiliatingly defeated by Tatsuya Suou and forced back into obscurity.
His Persona, Reverse Eros, has the same appearance as Lisa's initial Persona Eros, and uses earth based attacks as Eros does. His Persona, however, has a different color scheme when compared to Eros, as though it were negative (color wise).
Late in the game, he kidnapped Maya Okamura and took her into Xibalba to fulfill the Oracle of Maia, but got hit by one of the defensive laser traps, burning his face and killing him. His remains were found later by the party.
"Young producer of the group, Muses. His fortune of success came true... I feel I've met him before and detest him..."
—His introduction, Persona 2: Eternal Punishment
Sasaki is again producing the MUSES with the same members. Although not indicated directly, he is likely backed by the New World Order in order to increase his fame to present the seminar, with the intention of draining locals of their Kegare, the opposite energy of Ideal Energy. However, he is discovered by Maya Amano and forced to defend the Kegare stores in a violent shootout. Not too long after, though, the tanks are shattered and he is doused in the energy, transforming him into a JOKER, leading him to attack the player.