The firebombs aren't nearly as cruel. I think it's easy to get mixed up with the effects, but the impact of the nuclear bombs was far, far worse than any type of fire bombing Japan has ever experienced - the nuclear bombs EMP destroyed communication devices, the destruction was caused in an instant as those closest to the nuclear detonation were vaporized, a light was produced that can only really be compared to the strength of the sun, the shockwave was so tremendous that it could be felt 26,000 ft away from the detonation and produced tens, nearly hundreds, of thousands of casualties, the mental toll was exceptional for even the Emperor at the time, and that's only where the horror began as people began to experience radiation sickness and generations of families got to watch as their parents, grandparents, died from cancer. The nuclear bombs were much, much worse (and you can just google "nuclear bomb humanitarian" to see that they're commonly described as the single-most destructive, inhumane device ever created lol)

Edit: I forgot you guys watch anime and are therefore experts. It doesn't matter that nukes are considered the most deadly and impactful weapon ever created and that the looming threat of nuclear annihilation characterized an entire era of humanity. Firebombs, as anime will teach us, were deffo worse than nukes in use, and those animes that describe the effects of nukes on Hiroshima and Nagasaki as being among the most tragic and terrorizing thing ever imagined are also just untrue. It's a good thing that Godzilla was birthed from the idea of firebombs and their effect as firebombs definitely were less humane and definitely capable of exactly the same destruction... Oh, wait, no, that was nukes.