Originally, Ryouji shows up as a new transfer student, and befriends Junpei, Yukari, the protagonist and the other members of SEES. His cheerful and reckless dating attitude is also subject of much talk, even going as far as asking Yukari as well as Mitsuru on a date upon first sight. Aigis remained extremely cautious of him, however, constantly referring to him as "dangerous."
His true identity is The Appriser known as "Thanatos," and serves as the harbinger of "Death" being the mortal avatar of Nyx, the goddess of death that will bring about The Fall. He is also the older version of Pharos.
A battle with Aigis on Moonlight Bridge finally awakens his memories of this aforementioned true purpose. When the group gets there, they find a damaged Aigis, and an unconscious Ryouji. After he recovers, he tells them everything he knew, and expressed that he is tormented by the fact of who and what he is more than anyone. He gives the group a choice: they can kill him on the spot, and the Dark Hour will vanish, and they will forget everything, and return to their normal lives, or they can let him live. Either way, according to him, it is inevitable that the world will end at the hands of Nyx; only by choosing to kill them, will their world end in a somewhat "painless" fashion. Depending on the choice the player makes, they can either kill or let Ryouji live, each resulting in a different ending. During the discussion with the main character, he shows that his original form is that of Thanatos, the Ultimate Persona of the Death Arcana.