Demon Devourer

Weak. Frail. Powerless. That is all Guyeong Oh has ever been, until the legendary Demon Devourer chooses him as its successor. When the Hell Demon opens the Gates of Hell and unleashes monsters upon the human world, Guyeong is thrust into a war he never asked to fight. His only chance to stop the invasion is to devour every demon in his path, growing stronger with each one he consumes. Fortunately for Guyeong, nothing tastes better than monsters fresh from Hell.

(Source: WEBTOON)