One song that I wrote based on Pokemon.
There is a theory that you killed your Rival's Raticate.
You battle him with it on the S.S. Anne, and then the next time you battle him he is in front of a grave in Lavender Tower, this time he doesn't have a Raticate on his team.

So, the theory is that he didn't get to the Pokemon Center fast enough and the Raticate died, and then he buried it in Lavender Tower. Now, I could go into all the evidence, but I'll let you just explore it as you wish. Just go to youtube and type in Raticate's theory, and there you go.
Thanks and enjoy!~