I'm looking for a word opposite to dying [closed]

Perhaps the word rejuvenating.

This refers to something or someone gaining strength or vigour it once/previously had.

A living thing would revitalize.

revitalize (v): to make (someone or something) active, healthy, or energetic again; to give new life or vigor to.

A light would brighten or intensify.

A person would be recovering. A light would be intensifying. A houseplant would be perking-up.

‘regenerating’ or perhaps ‘reviving’

It's often used in sci-fi for example Dr.Who regenerates

This is really context dependent.

Who comes back to life? Why? How should we feel about it? Was he dead or just injured? Was this a physical or brain injury? Is the healing magical, mechanical or by providence?

I think you're looking for a word like kindling, which means to arouse or inspire, to start building a fire. It is the opposite of dying.