fallen angel; Lucifer
Primarily a Christian term referring to angels cast out of heaven, especially Lucifer. Also used in fantasy and anime contexts.
The fallen angel Lucifer is said to have once been the most beautiful angel.
The boss in this game is a fallen angel who fell into darkness.
Compound of 堕 (だ, 'fall, degenerate') and 天使 (てんし, 'angel'). The term is a direct translation of the Christian concept of 'fallen angel'.