Apocalypse: I Awakened from the Start

Also known as Star Source Users of the Apocalypse.

[Otherworldly invasion + a growing protagonist who becomes invincible later on + not a self-sacrificing saint + no System + no harem] On a sunny morning, Blue Star was struck by an unprecedented catastrophe. Alien races invaded, plunging the world into slaughter and terror as humanity’s numbers dwindled rapidly. The invaders took over Earth, and for the next thirty years, humanity lived in fear. Then Star Source Users emerged, giving people the strength to fight back. Six mighty human champions arose, and by working together, they reclaimed half their territory. They also built the Star Source Academy to train Star Source Users to fight the invaders, giving rise to countless heroes. Now, a young man arrives at the academy and begins his own legend.