Don't Be Afraid, I Just Have MAX Affinity with Godhead

My sister's illness is not a terminal illness, but a curse. She was sent to a special lunatic asylum, where every patient was listening to the god's last words and heading towards irreversible madness. To save her, I stepped into the shadows of the world and became dangerously aligned with a fallen being. They say I'm the only "key" to the madness. Therefore, the organization that houses the secret regards me as its most valuable asset, while the cult lurking in the darkness regards me as the perfect prey. Everyone wanted to take advantage of me, but no one told me the truth. But when the whispers of the gods began to echo in my ears, and when the countdown of my sister's soul continued to accelerate, I gradually realized - will this "key" open a door to hope, or will it release... The end that is imprisoned in the world?