(monarchy) an East Asian practice of dating, using exactly one distinct era name for each monarch's reign, where such era name also eventually becomes the monarch's posthumous name

system; institution

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

East Asia

an era name

history / the 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).

a target, a mark, a bullseye / an objective, an object (of doing something)

as far as ... is concerned; in terms of ...

feudalism (social system)