I'm a sucker for these, my dudes.

Idea No.1:
Time Period- Modern Day
Person A is a psycho/cannibal/etc and Person B is their nurse/caretaker in the asylum. Person A is very dangerous and hates Person B at first, but they slowly grow close to each other.

Idea No.2:
Time Period- Any
Both Person A and B are in the asylum for whatever reason and have cells across from each other. They communicate by sign language and Morse code, and in the showers/cafeteria. They plan a massive, bloody breakout together.