na-adjective, noun which may take the genitive case particle 'no', noun
immortal; undying; indestructible
Describes something that cannot die, be destroyed, or fade away. Used for abstract concepts such as fame, spirit, or legacy, as well as mythical beings. Often appears in the phrase 不滅の.
He left behind an undying record in the world of sports.
His achievements became immortal.
Some people believe in an immortal soul.
Many people believe that his spirit is immortal.
The composer achieved undying fame.
不変 means 'unchanging' and focuses on lack of change over time, while 不滅 focuses on not being destroyed or dying out.
不滅 means 'indestructible' and can describe physical things or abstract ideas, while 不朽 is reserved for cultural or artistic legacies.
Compound of 不 (ふ, 'not') and 滅 (めつ, 'perish' or 'be destroyed'). The kanji combination directly yields the meaning 'imperishable' or 'indestructible'.