In Shinto, a well on Fujiyama gaurded by Sengen bestowed this property.  One place where everyone had this quality forbade inhabitants from touching the soil of Ireland, lest they never return, and is ruled by Niamh in Celtic myth; that place, "Tir na Nog," is named for this property. A son of Olvaldi once caused the Norse gods to stop having this property by stealing Idunn's golden apples. This property was notably not given to a son of Laomedon who founded Susa in Ethiopia after running off with Eos. For 10 points, Tithonus turned into a cica
In Shinto, a well on Fujiyama gaurded by Sengen bestowed this property.  One place where everyone had this quality forbade inhabitants from touching the soil of Ireland, lest they never return, and is ruled by Niamh in Celtic myth; that place, "Tir na Nog," is named for this property. A son of Olvaldi once caused the Norse gods to stop having this property by stealing Idunn's golden apples. This property was notably not given to a son of Laomedon who founded Susa in Ethiopia after running off with Eos. For 10 points, Tithonus turned into a cicada because he was granted eternal life, but not what useful complementary property?
In Shinto, a well on Fujiyama gaurded by Sengen bestowed this property.  
eternal youth [accept obvious equivalents]