Melissa Marino

Melissa was a healer and Steve's wife, as referenced in his book. Though she technically never appears in person during the story, you can find multiple clues of who she is / was.

A painting of her can be found in Steve's house.

G0R5 (Steve's maid) has a permanent face expression is similar to Melissa's. One of the strongest enemies in the sewers, called "Marino", has a face that looks very similar to her's.