Godzilla vs. Little Boy revision 2

[Touchstone]

Someone told someone a story
about the cloud that rose above the water,

It's funny that you say "after I wrote it I thought this is probably Godzilla vs the Enola Gay" because after reading just the title and those first two lines that immediately sprang to my mind as being what you were writing about.

the light that dimmed the sun,

I understand what you mean but the physicist in me balks at that construction. Perhaps "the light that outshone the sun,"

only no one escaped
the rationalization that if we kill
there will be peace.

Taking this out of order, I love that part.

Survivors usually walk away,

I don't that works so well though because it implies that this time the survivors employed a mode of transport other than walking rather than that this time nobody's ideas remained intact, which is what I believe you're trying to convey.

I can't think of any great improvement to suggest but perhaps something like "Usually some survive," or "Survivors are usual,"

The cherry blossom
withers on the branch
echo of voices

I think that is superfluous.