Princess Rei

Princess Rei is a character from. She is a mystic female who was Charm Lord Orlouge's first princess. She escaped from Facinaturu twelve years prior to the game's events by committing suicide and being reborn into human flesh. Since then, she has maintained a low profile by working as a miko in Devin. Likely due to the mystical energies from all of the fortunetellers surrounding Devin, Orlouge is unable to detect her presence there. Any party member can visit her, but only Asellus can recruit her later on.

Asellus's Quest
If Asellus visited her old coffin while accompanied by Princess White Rose at the beginning of her quest, she can recruit Rei after escaping the Dark Labyrinth.

Other Quests
If the main character finished one of the Light or Shadow Quests and one of the Arcane or Rune Quests, she teleports the party to Kyrin Paradise to start the Space Quest. You can also ask her to draw lots (o-mikuji), but she always claims they're sold out.

Trivia

 * Rei is the only character to have the full complement of Mirage Magic.