interest

(monarchy) Japanese emperors and their 皇族 (kōzoku, “imperial relatives”)

history / the study of history

historic, historical / already-happened, past / former, old, traditional

oral history

historicism

historian

(Internet slang, especially anime and manga fandom) events or things from the past which one wants to whitewash/erase from history (due to it being embarrassing, poorly received, etc.); dark past

study of history

"Historical kana usage", a prescriptive method of using kana to write Japanese. Devised in the Edo period by Keichū (契沖) and taught in schools until 1946, it aims to be etymologically faithful and reflects earlier stages of the language (Heian period and earlier).