"I never dreamed of seeing that card with my own eyes... This is indeed a surprise... Behold the last power you and I shall unveil... It is the power to bring about a new beginning, or the ultimate end. It may be possible now, with this newfound power... You may be able to defeat the one who cannot be defeated. What you have in your hands is the power of the Universe... ...Nothing is outside the realm of possibility for you now."
The Universe Arcana (宇宙, Uchū)? is one of the most powerful Arcana in the Persona series. The Universe Arcana is commonly associated with Social Links, where its power is based upon the protagonist's bonds with others.
Much like the Aeon Arcana, the Universe is not part of the Rider-Waite Tarot Deck like the other arcana, rather, it is from the Thoth Deck, numbered XXI and replacing The World Arcana. The first and only known user of The Universe is the protagonist of Persona 3 where he was able to unleash its power to seal Nyx.
The Universe Arcana itself doesn't have a specific design. When Igor creates The Universe Arcana for the protagonist of Persona 3, all that is seen is an empty tarot card.
However, in Persona 3: The Movie, The Universe Arcana card had the same design as The World.
The Universe Arcana serves as catalyst of sealing Nyx in Persona 3. Knowing that Nyx cannot be defeated, the protagonist was taken to the Velvet Room. Igor comforted the protagonist by informing him that he is, in fact, still alive. He questioned the protagonist if he could hear the sound of his friends cheering him to not give up.
Through the voices and cheering of the others, Igor crafted the Universe Arcana and promptly gave it to the protagonist. Igor remarked that he never dreamed of being able to see the Universe Arcana, and tells the protagonist that it symbolizes a new beginning or the ultimate end. Awakening in the highest plane of Tartarus, where Nyx descended, the protagonist ascended towards Nyx's true body, the moon, in an attempt to stop the beginning of The Fall.
However, upon achieving the Universe Arcana, the protagonist was unable to unleash its power, due to Nyx's assault. Through the cheering of SEES and others, the protagonist managed to restore all of his energy through conjuring to perform the Great Seal, sealing Nyx away from humanity. However, using such tremendous powers required the protagonist to sacrifice himself, as the Great Seal used his life essence to seal Nyx away.
In the playable epilogue Persona 3 FES, The Answer, it is revealed that that the protagonist is not directly sealing Nyx, as she herself is not a malevolent entity. He instead exists as a barrier between Nyx and Erebus, the embodiment of all the world's sorrow -- in essence, the secret wish in the hearts of all to seek death. If Erebus touches Nyx, she will bring forth The Fall. Erebus constantly attacks the seal, though he remains barred by an enormous golden gate that the protagonist's soul guards.