In hindsight, Grand Fisher was a Menos without being a Menos, emulating the sheer power and boundless ambition of those superior Hollows despite being just one soul.

Source: https://www.cbr.com/bleachs-grand-fisher-hollow-why-so-special-rare/

Shrieker's name made sense given his sonic ability, at least, and it was soon horribly clear how Grand Fisher got his name, too.

Source: https://www.cbr.com/old-bleach-episodes-weirdest-details/

Then Isshin got a shocking glow-up when he became a Soul Reaper and killed Grand Fisher.

Source: https://www.cbr.com/best-bleach-character-improvements/