Pluto the Tormentor is a one of the bosses in in Shin Megami Tensei IV.
Pluto the Tormentor dwells in Blasted Tokyo. It is a machine sent by God to kill the remaining humans in Blasted Tokyo. It does this by spreading a vicious poison throughout Blasted Tokyo. Nothing seems to be able to stop this poison once it infects someone. Even dismembering infected limbs won't stop the poison from spreading. On top of that, Pluto also has an army of robots assisting it in its mission. There are three varieties of Pluto robots: Pluto Soldiers, Pluto Warriors, and Pluto Giants.
Flynn and his friends learn of Pluto soon after their arrival in Blasted Tokyo. A man named Akira sends them on a mission to go to Pluto Castle and defeat Pluto to save humanity, with the activation device for the Yamato Perpetual Reactor being their reward. Flynn and his friends accept the mission and go to Pluto Castle to find and defeat Pluto. When they find Pluto, they find that it speaks, but doesn't converse. It just parrots things like how Flynn and his friends aren't the Lord's Chosen and how it seeks to obliterate Filth in the Lord's name.
After Pluto is destroyed, Walter is the first to notice how much cleaner the air is becoming after Pluto's destruction. After Flynn and his friends return to Blasted Shinjuku to deliver the good news, Akira fulfills his promise and gives Flynn and his friends the remote for the Yamato Perpetual Reactor.
He then goes on about how the humans need passion and not empty words to restore Tokyo. He also states that after Tokyo is restored, he's thinking of renaming the city and decides to rename it the Easter Kingdom of Mikado out of respect to Flynn and his friends. Pluto is mentioned by the Ancient of Days in the DLC Challenge Quest, Ancient One of the Sun.