The cat and the rabbit is about Luca and Natsume from their childhood as recounted in chapter 62.

The Cat and the Rabbit

Was many a year,

When most lives fell,

The cat and the rabbit

Now have a tale to tell

In the foremost years

The rabbit was alone

The cat then asked

Why do you moan?

The 2 were friends

Forever to the end

But one was to be punished

And the other to fend.