Ruri'iro Kujaku is his Zanpakutō's true name. Ruri'iro Kujaku is an odd sword, as it has a favorite color. "Azure" is its favorite while "Wisteria" is its least favorite. Fuji Kujaku is a nickname that Yumichika gave it. Ruri'iro Kujaku really hates that name, so when Yumichika calls it that, his Zanpakutō sulks and doesn't reach full power. It is only when he calls it by its true name that its potential is achieved.