What values define a god? What delineates a god from a demigod? Or a demigod from a powerful immortal? How do you measure immortality? Is it power? Drive? Inheritance?

Celestia has, or at least had, all of these virtues. Twilight has the power and the drive, but not the inheritance. Celestia doesn't mind, she still loves her little Twilight like she loves all her little ponies. Even if Twilight doesn't have an outer god as a father like Luna and Celestia.

As the years go by, their relationship changes. As does Twilight...

Warnings (also spoilers):
No sex scenes. This is, oddly, not porn. There are lots of discussions about sex, though. And implied, or suggested, bad things. The one bit which might be construed as non-con is very much not, the character going into it knows exactly what she is doing.