Chenmo de Secai

The story of them happened in such an unexpected place, a mental hospital. To escape from the shadows of childhood, he thought he would hide for the rest of his life. But someone said to him, "I won't pull you out of the shadows, but if you want, I will stay with you in the darkness forever."

(Source: Webnovel)

Note: The author passed away before completing the story, so the artist finished the final chapters alone.