|Jafar says: Read my lips and come to grips with the reality!|
Erebus is the main antagonist of the epilogue of Persona 3: FES - The Answer and the overarching antagonist of Persona 3 as a whole.
Erebus was created by the lurking malice in all of humanity that wishes for death, and once it fully formed it would call upon Nyx to bring an end to humanity by enacting The Fall.
One Aegis won the Keys from the rest of S.E.E.S, they wished to see the miracle the Protagonist preformed that defeated Nyx and allowed humanity to keep on living.
They learn that he had used his own life force as a seal to seal Nyx away from humanity so she couldn't bring about The Fall, however Metis explains that sealing away Nyx is not necessary for she is neither hostile nor malevolent. The truth was the seal was place to keep Nyx from being touched by Erebus, the manifestation of the collective human desire for death. Yukari explains that when someone's life loses it's meaning, the thought of death becomes comforting, and Aegis confirms this by saying that during a time she too wished to learn death. Thus all the malice from their thoughts helped form Erebus.
When they defeated Erebus it dissolves, however it will reform unless that extremely small malice in all of humanity disappears forever.
Persona 4: Arena
Erebus makes a cameo in Persona 4: Arena being defeated by Elizabeth, she states that by the end of the year it will reform, confirming that it will never go away unless humanity stops wishing for destruction.
Snow Queen Quest
Victims of the Snow Queen Mask | Tomomi Fujimori | Night Queen
Masked Circle (Master Joker | Tatsuya Sudou | Junko Kurosu | Anna Yoshizaka | Ginji Sasaki | Akari Hoshi)
New World Order (Tatsuzou Sudou | Kiyotada Sumaru | Takahisa Kandori | Chizuru Ishigami) | Nyarlathotep
Persona 3 FES
Persona 4: Arena & Persona 4: Arena Ultimax
Persona 5 The Royal
Persona 5 Strikers
Alice Hiiragi | Ango Natsume | Kuon Ichinose | Mariko Hyodo | Akane Hasegawa | Akira Konoe | EMMA
Teru Gojuin | Dark Yashiro | Yatsufusa Hatanaka