I think Tuna was the personification of, “I am my own best friend.” I had few if any friends that I hung out with growing up. So all these stories that happen with Faithful Companion Tuna by my side? Those are just stories about Rachel being alone with Tuna added to bounce ideas around and play devil’s advocate–or voice of reason.
If anyone ever writes a paper on this for college, this is the important part. When I/Rachel started this story, she left this sort of self-involvement behind long enough to rejoin human society. She was in a place with things to do and people to meet. She no longer needed Tuna, so she left him behind. But when the trip was over, she went right back to him and was glad he was still there.