The rains of Castamere aka the Lannister song talks about the destruction of the House Reyne by Tywin Lannister. Tywin Lannister sabotages the house Reyne and the song is sung from his perspective.

TLDR -; After the destruction of house Reyne and as the rains poured down at Castamere , there was no people/soul to hear the rains as everyone were killed by the Lannister army.

The song title “Rains of Castamere”is the wordplay on the house Reyne. Let us see some history before getting into the song breakdown. House Reyne and Lannister have pledged themselves to the king on the throne. It was the time when Cerci was young and Tywin’s father Tytos Lannister was ruling at the Casterly rock as Roger Reyne was at Castemere and Castamere was Reyne’s stronghold as Casterly rock was to Lannister’s.

Roger Reyne claimed that Tytos Lannister was very weak and too feeble to rule , and started a rebellion against them. Tywin Lannister, a young prince at that time stood against the rebellion and crushed Roger Reyne to death and destroyed the house Reyne. Thus the song is the aftermath of the victory of Tywin over house Reyne.

The song breakdown:

The song is sung from Tywin’s point of view, where the initial lines are to be like Roger Reyne demanding an explanation to Tytos, after a certain point on the song, it describes what happened to Roger and the house Reyne. Lets breakdown,

And who are you, the proud lord said,
that I must bow so low?
Only a cat of a different coat,
that’s all the truth I know.

Roger Reyne questions Tytos, why he should bow to the Lannisters. Here the Roger Reyne is assumed to the proud lord. The next lines,

Only a cat of a different coat,
that’s all the truth I know.

House Lannister and Reyne have a similar coat of arms, the “Lion”.

In a coat of gold or a coat of red,
a lion still has claws

COA of Reyne’s was a lion of red coat whereas Lannister’s is a lion of golden coat. Here are the reference images below,

  1. House Reyne:

2. House Lannister :

Though Lannister’s may have a coat of gold, both the lions have same claws, the next two lines describes about the claws of the lions.

And mine are long and sharp, my Lord,
as long and sharp as yours.

Moving on.

And so he spoke, and so he spoke,
that lord of Castamere,
But now the rains weep o’er his hall,
with no one there to hear.
Yes, now the rains weep o’er his hall,
and not a soul to hear.

Tywin mocks that , though Roger Reyne — Lord of Castamere spoke of this hall, as the battle has ended now and as the rains pour over the Castamere halls, there are no one there to hear the pour of the rain.

The last line is even more worse and denotes that the house Reyne was sabotaged and crushed to the ground as

Yes, now the rains weep o’er his hall,
and not a soul to hear.

Thus Tywin’s rose to fame and “Rains of Castamere” became the Lannister Song.

There was an explanation even in the TV Series, in season 3 , episode 8 titled “Second Sons”, Cerci warned Margery by narrating the reason for the song and would eventually strangle her to death , if once Margery calls Cerci her sister again. Typical Cerci. Here is the link to those who have missed it.

https://www.youtube.com/watch?v=iQ2QP4hfs5s

Hear Lannisters roar ;-)