Ruby is one of the anti-antagonists that killed Ryuji's body. She tried to hide her crimes, but to no avail. While playing the Persona Nonary Game, she was to make one option of the two. One, you beat the game. Or Two, you confess. She chose one. Eventually, her crimes were exposed. She killed off Ryuji's body because she wanted to make her "boyfriend" to come back to her, even though both weren't dating at all.
Persona: Itzpapalotl