The setting was in a closed apartment? Similar to a prison? The mc takes care of a convenience store. The ML is a kind like a top dog there. I don't think it's horror, leaning towards psychological.
I appreciate anyone who's trying to help~~
Red Mansion (▰˘◡˘▰)
Link: https://www.mangago.me/read-manga/red_mansion/
Also I'm tearing up seeing Sugishita hesitate to come near Sakura. It must have been devastating to see Sakura curled up under his blanket all alone.