Leaping_Patriotic_Autumn; Wikipedia/commons
The meaning of the word kokutai is (intentionally) broad and vague. It was used to justify authoritarian acts by the Imperial Japanese government.
“Kokutai is a vague but emotionally powerful term for the mysterious national essence of Japan, which finds more concrete expression in such things as an unbroken line of sovereigns, loyalty and filial piety, obedience to the emperor, and a variety of Japanese cultural habits or characteristics.”