Prodeus

In the future, humanity harnessed power from a hellish dimension which they used to become technologically advanced, some even used the power to become a new species called the Prodeuns. The Chaos, the monsters from the hellish dimension learned of humanity and opened a portal to the universe to destroy Earth. Most humans were killed after quickly losing the war, the Prodeuns then took over humanity and forced everyone to become Prodeuns, but a small group fled on a ship and came up with a plan to get to the Prodeuns base to defeat them and Chaos.
However, everyone except for the protagonist of the game (only known as the Prodeus Agent) is killed by Chaos and the Agent is forced to finish the mission himself. The Agent tries to break into the Prodeun’s base but is turned into a Prodeun instead, but he survives and gains access to a train. The Agent travels across the ruined land, destroying key facilities to both the Chaos’ and Prodeuns’ war effort, the Chaos try to freeze the world by using a space station but the Agent knocks it off course.
The Agent eventually makes it to the Prodeun’s base and weakens them enough, he then goes to the Chaos’ dimension and kills their leader, The Hunter. With the Hunter’s death, all of the Chaos are forced back to their dimension and are permanently sealed away. The Prodeuns inherit the Earth and the Agent travels through a portal to a utopian dimension.