Both are revenge stories with a female lead. Both heroines have had their lives stolen from them and seek to right wrongs.

Both involve ghosts that inhabit another person's body to figure out the mystery of their deaths. In Who Are You?'s case it's a father that inhabits the body of a cold young man. The father attempts to make things right with his daughter as they had a falling out before he died. In the process the man who's body the father inhabits falls in love with the daughter. He and the father team up to protect the daughter from whoever killed her father while they solve the mystery.

It's really really funny and the romance is sweet as well. I think the whole possession concept is handled a little better in Who Are You than in Oh My Ghostess.