Ouroboros is an ancient symbol depicting a dragon or a serpent swallowing its own tail to form a cycle. It is a very important religious symbol over the ages. In alchemy, it is a purifying sigil. The myth of the Ouroboros is not dissimilar to other myths of cosmic serpents, such as the Australian Aboriginal myth of the Rainbow Serpent. The image of Ouroboros crossing itself into an infinity symbol is a modern idea, but one that retains the meaning of endlessness.
"A dragon that signifies eternity. In biting its own tail, it forms a neverending circle. In alchemy, the art of Hermes, it is considered an important material to create the Philosopher's Stone. Some of Ouroboros' aspects are similar to those of Oceanus in Greek lore and the Biblical Leviathan."
—Shin Megami Tensei: Strange Journey Compendium
Ouroboros is a boss in Sector Eridanus. Its name is mentioned as Ouroboros Maia, making her one of the of the three Mothers of the Schwarzwelt (alongside Tiamat and Maya) you obligatorily fight. She dwells in the Vanishing Point Chamber, in the very core of Eridanus' top floor.
Ouroboros is fought twice; in her first form, she will continually regenerate health and use Wild Thunder, a potent Lightning-type attack, and Disaster Cycle, a light physical attack against all enemies, which has the added issue of liberally inflicting any possible ailments to the targets. Overall, the first battle is mostly difficult because of her ability to replenish her health.
However, it becomes apparent Ouroboros is simply immortal in this form, forcing the Strike Team to leave; Captain Jack is the one to call the Protagonist and point him to the exact locations from which Ouroboros is drawing energy. Once the demons at these locations are dead, Ouroboros will be dismayed about the "torus of eternity" being severed, and enter a second and more dangerous stage when the protagonist again enters the. Chances of seeing Disaster Cycle greatly increase and Ouroboros begins using Wave of Death, a potent physical attack.
Once she dies, she will moan in agony about the "holy realm of the gods" being defiled by humans, and leave behind a band of energy, pocketed by the protagonist, and her rare forma.
Also after defeated, Ouroboros is unlocked to special fuse using five demons: Dzelarhons, Kwancha, Mandrake, Basilisk and Vouivre.