Kanji and meanings
I’ll explain the meaning of Rengoku Kyojuro’s family name. It’s very powerful name which is eligible for the Flame Hashira! 🔥
REN means to smelt metal or train oneself.
The left part of this kanji stands for fire.
GOKU means hell.
The word RENGOKU is catholic purgatorium, a place between heaven and hell. A soul of the dead is purified with fire there. That’s why the kanji character with fire meaning part (REN) is used for this word when it’s translated into Japanese.
Given these background, we can say Rengoku Kyojuro’s flame is purification fire.