A medieval-themed world, where sorcery is somewhat common. Beyond elemental magic, there is also magic drawn from a perfect, heaven-like dimension ("light" magic), magic that can corrode and corrupt existences ("shadow" magic), magic that alters the state and perceptions of sentient beings' minds ("psychic" magic), and magic that warps the time-space continuum.
The story would follow a young mage prodigy's struggles with his immense potential and idealistic upbringing. Unable to come to grips with his Messiah complex, his affinity for shadow and psychic magic, and his inability to help everyone around him, he slides into madness and eventually creates a powerful artifact that grants him the ability to siphon magic from alternate dimensions.
With this power, he forces the entire world to bend its knees and live under his dictatorship, where he seeks to use his near-omnipotence as a weapon to eliminate evil and make the world a better place.
The story then shifts to a group of freedom fighters made up of his old friends, who believe that the main character's radical approach is wrong. They try to stop him from draining magic from alternate dimensions, and also free the world from his iron grip.
World with magic. Upstanding hero slowly becomes like Light, reaches god-like level of power, his old friends try to stop him.