Ambrosia

Ambrosia (アムブロシアー) is a small magic fruit that appears in the world of Toaru Majutsu no Index.

Concept and origin
The name comes from the of Greek mythology, where it is often times referred to as either the food or drink of the Greek gods, that confers ageless immortality upon whoever consumes it.

Principles
In the Toaru Majutsu no Index it appears as a small cone-like fruit that when consumed gives whoever has eaten ageless immortality, making them forever appear in whatever form they have upon consuming it. The effects of the ambrosia not only gives the one who has eaten it leave from death of old age, but apparently any form of death as well, terrestrial or extra-terrestrial, as Ladylee Tangleroad personally experienced.

Moreover, any one who has eaten the fruit can never use magic on their own, as it twists the cycle of their life force necessary for creating magic, as such one requires others to do magic for them.

It is unknown if the Imagine Breaker is able to negate the effects of ambrosia.