Anima Mundi is the final boss of Trails in the Sky the 3rd. It is the manifestation of the negative energy of Kevin Graham's Stigma, while taking the form of his guilt over the death of Rufina Argent. It states that it is the core of Phantasma; its very essence, while posing as Rufina because of Kevin's desire to be punished.
When the Aureole was separated from the Recluse Cube, the cube itself underwent changes, altering Phantasma to suit its autonomy until salvaged and coming in contact with Kevin. At that point, it started to bring forth his desires to be punished for his weakness and cowardice towards his past. The Cube, in tandem with Kevin's thoughts and desires by part of his Stigma, locked away the dormant copy of Celeste D. Auslese and her powers and gained control as the Lord of Phantasma.
During the final arc of the game, the Lord of Phantasma reveals itself to be Rufina, while Ries rejects it, saying that Rufina would never do the cruel things that it does to punish Kevin. Kevin and Ries are then brought to the Phantasma manifestation of Gehenna, where Kevin re-encounters his past as a heretic hunter and the people he killed, including Weissmann, the Faceless. Weissmann tempts Kevin into giving into being a superhuman for the sake of escaping his past, but Kevin declines, and unlocks a positive manifestation of his Stigma, the Holy Spear of Ur, and uses it to beat back Weissmann and the guardians of the gates of Gehenna: the fiends Astarte and Rostrum.
After finding that Rufina has left the seven planes of Phantasma and is located outside of them, in a giant wasteland with a single castle known as Phantasmagoria. Inside the castle, many angelic beings and creatures await, being reminiscent of the cathedral in the Holy City of Arteria. When Kevin and Ries reach the inner sanctum of the Great Gate, they confront Rufina once more, with Kevin revealing that he has pieced together that the Rufina in front of them is nothing more than a copy born from his memories, given form by his Stigma. The Stigma is surprised, not knowing Kevin had found out. It then introduces itself as Anima and claims its powers and rule over this plane; stating that it is the very core of Phantasma. The split groups are attacked by various large monsters, with Anima Mundi threatening that should any of them lose, their very beings will be devoured by the land. After the monsters are defeated, Anima attacks the party as the final battle.
When defeated, it explodes into a bright light, leaving only the Stigma behind, revealing that it has been cleansed and changed to a blue color.
Anima Mundi has an appearance of a fiend, with a ghostly female appearance at its core (likely representing Rufina), two large butterfly-like wings, massive arms, pelvic fins and a spike-like tail. Behind it is a floating, spinning representation of Kevin's Stigma.
During the battle, it will change color (Change Element) of both itself and the background and start a new phase, while still using some of the previous phase's attacks.
Starting phase: It can summon 7 pillars during battle, which all cast an art that enables Anima Mundi to use a battlefield-wide craft that does severe damage to the party: Sept-Crisis, all while making Anima Mundi immune to everything while they're upholding its barrier.
It can also attack with Air Cleaver - Yin, and inflict faint, as its most used attack.
Red: Templar Sword Zek Wo: Summons a giant Templar sword that does damage in a line and inflicts delay. It will also summon two Grand Grimoires via Summon Fiend.
Blue: Demonic Bow Nag Rub: It can attack with its crossbow bolt to inflict freeze, and increase its defense. It will also summon Grand Grimoires during this phase as well.
Gold: Rending Sound Shimehda: It can cause a battlefield wide impede on arts.
During any point after its HP drops to 50%, it can lower its DEF/ADF and will cast its S-Craft: Stigma Cannon Megidelus, dealing possibly fatal damage to your entire party and blowing away most of the battlefield, on top of inflicting MOV-down on the survivors.
- Anima Mundi is latin for "World Soul", the belief that there is an intrinsic connection between all living things on the planet, which relates to our world in much the same way as the soul is connected to the human body. This fits Anima Mundi, seeing as it claims to be Phantasma's very essence, and controls all illusions within it.