Anime Insider, October 2008, asked the question outright: is there a reason the manga is called Bleach, or is it a secret? Kubo answered in full: the color you associate with the Soul Reaper is black, but black is too straightforward, so he thought about white, but white is too simple, and bleach is the word that makes somebody associate white. That is the entire documented origin, a color two steps removed. At San Diego Comic-Con the same summer he told the panel the series itself began with an image, not a plot: he wanted to draw Soul Reapers wearing kimono, something nobody had seen before.
Kubo wears his record collection in the margins: volume-opening poems, chapter titles that nod to songs, a heroine named after a Scorpions-era aesthetic. So the fandom's favorite alternative origin is that the title comes from Nirvana's 1989 debut album Bleach, a claim repeated across fan wikis and listicles for two decades. Kubo, who has explained nearly every naming decision in the series when asked, has never confirmed this one.
Fan exegetes offer a third answer: bleach is what the Soul Reapers do. A Hollow is not killed but purified, its soul washed clean and sent on, so the title describes the cosmology's core process, sin bleached out of souls. Others push further and read the whole series as a meditation on whiteness, blank masks, white bones, the white desert of Hueco Mundo, the white-clad Quincy, with the title as the theme in one word.
The author says the title is a color clue. The fans say it is a Nirvana album or a theology of clean souls. Why does a story's name resist its own author's explanation?