Otherwise known as the Lady of the Lake, she is famous in English lore for giving Arthur the blade Excalibur along with enchanting Merlin and raising Lancelot after his father's death. In England, she was slain by Balin.
Vivian was released during the 2014 White Day event as a summon PG and later as a regular double-fusion. She is the focus of the permanent event The Lady of the Lake's Cunning Lie.
Shin Megami Tensei: Strange Journey
"A beautiful faerie of Arthurian lore. She also guards Lancelot, knight of the Round Table. She lives beneath an illusionary lake in France and is also known as the "Lady of the Lake." She is known for giving Excalibur to Arthur and for raising Lancelot."
—Shin Megami Tensei: Strange Journey compendium
Vivian appears as a common enemy in certain parts of Sector Eridanus. Finding Vivian and talking to her is part of one Thoth's EX Missions.
Shin Megami Tensei IV
Vivian can be found in the Infernal Tokyo version of Camp Ichigaya. She can teach Flynn the Lullaby, Mabufula and Estoma Sword skills through her Demon Whisper.
Shin Megami Tensei IV Apocalypse
Vivian can be found in Ikebukuro. She can teach Nanashi the Lullaby, Sukukaja, Dark Sword and Mabufudyne skills through her Demon Whisper. She benefits from learning Ice, Light and support skills.
Devil Summoner: Soul Hackers
"A beautiful faerie of Arthurian lore. She also guards Lancelot, knight of the Round Table. She lives beneath an illusory lake in France and is also known as the "Lady of the Lake." She is known for giving Excalibur to Arthur and for raising Lancelot."
—Soul Hackers 3DS compendium
At maximum loyalty, Vivian can be transformed through Mystic Change into Lancelot's Sword.
Persona 2: Innocent Sin
"Lake fairy and guardian of Lancelot in Arthurian lore."
—Persona 2: Innocent Sin Profile
Devil Survivor 2
"A beautiful faerie of Arthurian lore. She guarded Lancelot, a knight of the Round Table. She lives with many knights and servants beneath an illusory lake in France, and is known as the "Lady of the Lake." She gave Excalibur to Arthur."