Saya no Uta

Fuminori Sakisaka has a traffic accident that kills his parents and leaves him severely injured. After life-saving brain surgery, his perception of the world changes: everything he sees becomes blood and guts, people's looks and voices seem like monsters, and food that generally appeals to him tastes disgusting.
As he contemplates suicide in the hospital, Fuminori meets a mysterious pretty girl among the flesh-covered world. She introduces herself as Saya and is looking for her father. Due to their circumstances, the two become close and move in together, becoming lovers and incredibly dependent on one another.