Fenrir was prophesied to kill Odin during Ragnarok, so Odin bound Fenrir to his throne. At Ragnarok, Fenrir will escape and kill Odin in revenge for his imprisonment. Another name for him is Vánagandr.
"Origin: Scandinavia. A giant wolf appearing in Norse mythology. His other name is Fenrisulfr, one of three children of Loki and Angraboda. His mouth can open so large that it can envelop the heavens and the earth. It's prophesized that he will eventually swallow the sun, and so he was bound. When Ragnarok begins, he will be released, the gorund will open, and he will eat Odin."
"A gigantic beast of Norse mythology that swallows all. He takes the form of a wolf so big that when he opens his mouth, his jaws touch the earth and the sky. Blazing flames erupt from his eyes and nose. He was counted along with the world serpent Jormungandr and the goddess Hel as one of the three children of Loki, the god who would later trigger Ragnarok, and the giantess Angraboda. At birth, Fenrir had no particular powers at all and was not placed under the watch of the Aesir. But as time passed, his power grew. At last, the gods attempted to bind Fenrir with a chain called Loedingr, but Fenrir easily bit through the chain. The gods then tried again with Dromi, twice as strong as Loedingr, but again Fenrir easily broke it. Finally, the gods asked the dwarves to forge a third chain, Gleipnir ("entangling one"), and with this they succeeded in binding Fenrir. At Ragnarok, Fenrir will break free from Gleipnir and swallow Odin, the chief of the gods."
—Shin Megami Tensei IMAGINE Compendium
Fenrir can only be acquired through fusion. Enemy variants can be encountered within Suginami Tunnels' gold-level instance and within the final boss room for the Suginami Unknown boss rush. He is also the final boss of the Azura's Special Training storyline quest where he is accidentally summoned instead of a Kodama. Fenrir is among the mountable demons within the game.
"A giant wolf creature of Nordic lore, son of the evil god Loki. Fenrir is destined to kill Odin at Ragnarok. On that day, his magical bindings will be broken and he will rise against the Aesir in combat."
—Devil Summoner: Soul Hackers 3DS Compendium
Fenrir can be recruited as an ally in the underground ruins in Soul Hackers, or alternitavely created by fusing Haunt Vetala and Yoma Peri in the Gouma-Den.
Devil Summoner 2: Raidou Kuzunoha vs. King AbaddonEdit
Fenrir appears as both a demon and the sword Vanargand (ヴァナルガンド).
"A giant wolf creature of Nordic lore, son of the evil god Loki. Fenrir is destined to kill Odin at Ragnarok. On that day, his magical bindings will be broken and he will rise against Aesir in combat."
—Devil Survivor 2 compendium
Fenrir appears as the strongest member of the Beast race.