Board Thread:Naruto Discussions/@comment-25691159-20200529162803/@comment-25691159-20200608130715

Also fourth databook entry on Kagutsuchi:

“Immortal black flames turn into a blade of flames that mows down life!!

A ninjutsu where form manipulation is added to the never disappearing immortal flames that are "Amaterasu". In his fight with the Raikage, Sasuke was forced into a predicament and in that moment, he created this technique. Like "Amaterasu", it's a ninjutsu only those who awakened the "Mangekyo Sharingan" can use, changing the flames into a sharp blade to greatly increase their killing power. Not only is the enemy burned by "Amaterasu", he also suffers burn damage instantly. By regulating the form manipulation, it's even possible to use the flames as a throwing weapon to attack from afar.”

Clearly implies that Amaterasu won’t extinguish with any passage of time.