Sinui Namja

The priest Benz, who was about to turn his back on the world due to intense guilt and despair, is stopped in his tracks by a blinding white light at the moment he pulls the trigger of a rifle. He believes it to be a god, hanging from the attic ceiling. Surrendering his body and mind to this 'god' with serpent-like tongues and glowing tentacles, Benz becomes increasingly dependent and fully dominated by it.

(Source: Mr.Blue, translated)

Note: Chapter count includes 6 side story chapters.