great impropriety (toward the imperial family)
Archaic term for a serious breach of etiquette or disrespect directed at the imperial family or related institutions.
In the Edo period, acts considered great impropriety toward the imperial family were severely punished.
crime against the imperial family (or related shrine)
Historical legal term, often associated with the 八虐 (eight unpardonable crimes) in ancient Japanese law. Refers to offenses against the emperor, imperial family, or imperial shrines.
See also: 八虐
Under the ritsuryō system, great disrespect toward the imperial family was counted among the eight unpardonable crimes.
From Middle Chinese 大不敬 (dà bù jìng), meaning 'great disrespect'. The term was adopted into Japanese legal and historical vocabulary, particularly in the context of the ritsuryō codes.