Yume has a small stature and petite body. She has short purple hair that ends with a small tilt and reaches her shoulders and dark blue eyes.
She is seemingly always wearing a black headband with two ribbon-shaped symbols on each side and also has Light Blue eyes. When Lilith, the Succubus residing within her takes over her body, she grows a dark purple tail that ends with a reversed heart-shaped symbol, and when needed, a pair of wings that have the same color as her tail, but with purple horns at the top.
After enrolling to Tensou Academy, she also often wears the school's uniform, consisting of a white one-piece sailor suit.
Yume is the vessel of Lilith, the world's strongest succubus.The bullying Yume had gone through because of her mind-control magic made her think that her existence will always cause problems and harm to others, and she could not kill herself in a simple way because Lilith would simply find another suitable vessel and that person would also have to suffer. So she decided to assist Taishikyoku in their plan to control Leviathan, the strongest living weapon from the ages of the gods as she is the being with the strongest mind-control magic, only to betray them and reveal her true goal which was to die inside Leviathan, which has the ability to dissipate any entity into nothing and which will kill her along with Lilith.
The Black Sword Shaman
Yume was confined in a facility on Blue Elysium, where Sayaka attempted to rescue her. After running a fair distance, Sayaka senses a formidable opponent, and instructs Yume to separate and look for Kojou.
Yume later meets Kojou at a lifeguard center. She follows him to his part-time work place, causing brief confusion with Asagi. She soon revealed her circumstances to them, before crying herself to sleep. While bringing Yume to their cottage, Asagi suggested they buy some clothes for Yume, who was still in her swimsuit.
Bride of the Dark God
Yume visits Saikai Academy in the afternoon to show off her new uniform to Kojou.
The Fugitive Fourth Primogenitor
Asagi, Motoki and Yume rendezvous at Kojou's apartment before making their first temple visit of the year.
The War Of Original Vampires
Never-ending Night Banquet
Mind Control: Succubus or "Mumas" are know to be able to control people's minds by making their deepest desires go berserk. And Yume, who is the vessel of the World's Strongest Succubus has an exceptionally strong mind-control magic which can even control legendary creatures.
Pacification: This can also count as a mind controlling ability, whereas Yume/Lilith starts humming a certain melody which activates a mind control magic strong enough to pacify Leviathan, a living weapon from the age of the Gods. This ability has been known to generate a strong yellow light from the user's body.
- The name Yume means "tie, bind" (結) (yu) and "pupil of the eye" (瞳) (me).
- Yume's surname Eguchi means "bay, inlet" (江) (e) and "mouth. entrance" (口) (kuchi/guchi).