Japanese has a clear literary register, 古語 (kogo, 'old words'), that derives from the language of Heian-period (794–1185) court literature and the Edo-period (1603–1868) bushi (samurai) class. Modern spoken Japanese is grammatically and lexically different — different copulas (なり vs だ), different negation (ず vs ない), different vocabulary (よもや vs まさか) — but every Japanese student studies 古文 in high school, so the patterns are recognisable to literate adults even when no one would use them in conversation.

Manga and anime exploit this gap as a casting device. Drop a single 古語 marker into a character's dialogue and you immediately code them as one of: an immortal (demon, god, supernatural elder); a samurai-coded protagonist evoking older martial virtue; a noh / kabuki / chanbara reference; or a comic stuffy intellectual. Rengoku's 「よもやよもや」, his 「ぞ」 sentence-finals, his preference for 「貴殿」 over modern 「あなた」 — these are all 古語 / 雅語 (gago, 'elegant/literary words') markers that paint him as a Taishō-era man whose mental model of being a Hashira is taken from Edo-period samurai code, not from the modern military around him. The effect compounds with his masculine register; together they produce 'samurai stage actor at the dinner table.'

English has no clean equivalent. The closest moves are Shakespearean affectation ('forsooth,' 'thou art'), King James biblical English, or fantasy-novel formal register ('I shall not forsake thee'), but each of these carries baggage that 古語 in Japanese does not. The result is that translated dialogue almost always flattens this dimension out — the character still sounds like they have a 'voice,' but the era and class signalling is gone.