The male leads are both being surrounded by spirits. But also their differences make both series unique. "7 Days Before Valentine" surrounds Sunshine who needs to understand that the world doesn't revolve around him rather to understand who we are and what our purpose is, while at the same time knowing others and understanding them as well. In "The Whisperer", the male lead Khun has always been told that he's crazy and only does "bad things". However, he won't seek revenge towards those to have lied to him, rather show them what "crazy" really is.

In "The Whisperer" the lead actor has to live it's daily life tormented by ghosts of his relatives. The lead in "Dear Doctor I'm Coming For Soul" has the ability to see a soul reaper take life from his patients and other people with the ability to do nothing about it, like in "The Whisperer" both leads of both series have to live with dead spirits haunting and tormenting them.

Both are really enjoyable series with their similarities and differences!

In both series, the mains are living with ghostly spirits their daily lives.
The story is not exactly similar, but if you want another interesting, horror drama, this is the one for you!