WARNING: The following contains spoilers for Platinum End Episode 13, "World Peace," now streaming on Crunchyroll and Funimation.
The heavenly battle royale in Platinum End can only have one winner, and that being, who will become the new God, can reshape human society as they see fit. Kakehashi Mirai aims low, intending to live a quiet life of happiness while his worst enemy, Metropoliman/Uryu Kanade, aims to radically alter human civilization to fit his own views.
Many people daydream about how they would change society -- often for the better, such as ridding the world of hate, crime and war. Metropoliman claims to want equality and peace for all, but at an extreme cost. He wants to eliminate the impoverished masses to benefit the wealthy elite, and as Episode 13 reveals, this quest is personal as well as political.
Metropoliman and Mirai continue their feud at the abandoned amusement park after Mukaido Nanato's wife and daughter are rescued, but Metro's aims go far beyond taking hostages and killing his rival God candidates. To him, this battle is just the first step toward a revolution, a future where no one must pay for the benefit of others -- no taxes, no welfare, no charity, no altruism of any kind. Metropoliman favors the elite class of beautiful and wealthy people and believes the burden of charity tarnishes that beauty. However, Metropoliman's goals aren't merely political; his little sister Uryu Rea's demise ties into all this, and the wounds are clearly still fresh in Kanade's mind.
Kanade takes great pride in being the son of a wealthy family, and a flashback shows he gets along well with his beloved little sister. He prizes their attractive appearances, viewing Rea as a pure, delicate maiden to be shielded from all impurities -- including potential boyfriends. These protective feelings become possessive and dangerous when Rea mentions her intention of dating a boy whom she knows, and Kanade protests.
Attempting to restrain his sister, Rea falls to her death, for which Kanade blames himself. He has her body preserved to maintain its beauty, then sees her as an analog for the entire elite class that must be protected. Kanade has already failed his sibling, but he might not fail the entire elite class.
Uryu Kanade has a somewhat arbitrary and subjective view on what constitutes an elite person who must be protected from the masses, which makes the fight personal for him. If he becomes the next God, he can ensure that all the Reas of the world have nothing to fear and can live in a peaceful, perfect garden world free of impoverished and needy people who would weigh them down. Kanade's vision in Platinum End is classism at its peak, aiming to exterminate most of the world's population for the benefit of a select few. According to Meyza the angel, Kanade would have to work with some conditions, but otherwise his plan is feasible, significantly raising the stakes of this heavenly battle royale.
Mirai fought and succeeded in protecting thousands of civilians from the wrath of the virus-loving fighter Kohinata. But Metropoliman won't go down so easily, and he threatens the vast majority of humanity with his radical scheme to create a perfect place for the beautiful elite. This terrifying plan can become reality if he takes Mirai's squad down, meaning the Platinum End protagonist and his fellows are all that stands between the world as they know it and class-based genocide. Therefore, Mirai must shed all fear and doubt to become the fighter the world needs him to be. Billions of lives rest on his shoulders.