Pluto (プルトー, Purutoo) is a demon in the series.
God of the Underworld, he is the Roman counterpart to Hades. The dwarf planet Pluto is named after him.
Shin Megami Tensei IV
Also known as Pluto the Tormentor, or the Tormentor for short, it is a machine programmed to eliminate all the filth that were not chosen by The Lord 25 years ago. It spreads poison throughout Blasted Tokyo that pollutes the air, forcing people to wear goggles and gas masks. it also creates the Pluto Soldiers to hunt down the filth and guard Pluto Castle, its fortress. Once someone has been infected by Pluto's poison there is no way to cure them and cutting off the infected limbs does not stop it from continuing to spread, leading them to become weaker and weaker until they finally die. Both Akira and Kiyoharu have been infected.
Pluto's name comes from people naming it after the Roman God who ruled the Underworld, rather than it being one that The Lord chose for it. Smaller versions of Pluto guard the Castle. The smallest, Pluto Soldiers, attack en masse when the Samurai first venture into the edifice, and later, they and larger versions, Pluto Warriors and Pluto Giants, occasionally pop up either in hordes or as part of attack groups.
The Samurai first meet Pluto on the basement floor of its castle, where poison spews forth from its eyes and its head. It speaks, but it does not converse, merely parroting how they are not the Lord's Chosen and seeks to obliterate them in the Lord's name. As the battle progresses it calls them filthy ones and that sins must be punished. Taking even more damage it attempts to make them think of its purpose, which is to serve the will of the Lord, but Walter tells Jonathan not to heed its words. Further into the battle it repeats its words, adding that destroying it is blasphemy and tells them to repair its functions. As Pluto loses its voice begins glitching, causing it to become extremely distorted and glitchy as it repeats insane commands to die before crumbling.
Interestingly enough, the Ancient of Days refers to 'Pluto' as such when it appears in the DLC. Ironically, this makes sense since in Christian faith, granting names to things is one of humanity's purposes in the universe.
Devil Children White Book
Pluto can be bought at the Casino for 5000 coins.
Shin Megami Tensei IV
Devil Children: White Book