1.
eternal youth and immortality
The state of never aging and never dying. A concept found in mythology, religion, and fiction. The four-character compound literally means "not aging, not dying."
Common patterns
A four-character compound (四字熟語) formed from 不老 (not aging) + 不死 (not dying). Can also be used as a no-adjective: 不老不死の体 (an immortal body).
Cultural note
The quest for 不老不死 is a major theme in East Asian mythology. The legend of 徐福, sent by the Chinese emperor 秦の始皇帝 to find the elixir of immortality, is said to have brought him to Japan. The concept also appears frequently in anime, manga, and fantasy fiction.