It does sound like something that would be a common epitaph phrase right? I could have sworn I had heard it before too, so I did a google search as well and came up with nothing non-Cross related. I think it just sounds familiar to us because we are familiar with it already.
On a sort of related note, I once saw some idiots arguing at gamefaqs about whether or not Serge's mom and Wazuki were his real father and mother, because they interpreted the "what once came from the sea" quote not as a metaphor for death but as a literal "they found Serge floating in the sea as a child." lmao