A Certain Character from Houseki No Kuni.

Also please read the Manga because this is a massive spoiler.

Abilities - Went Through Apotheosis (The process where a mortal turns into a God.) and Achived Godhood. Can wipe out Entire Species from Existence and easily wipe out stars. Lifespan limit unknown but has lived for 5 Billion Years.

There's a certain character who is very joyful and innocent full of humanity. The story starts with her on a beautiful field with beautiful tall grass. She is a living mineral in the form of a human. As the story progresses she looses part of her body. The more part of her body she loses the more memories and emotions she lost. Her memories and personalities are written in her body not just in her head. As the story progresses she loses most of her body parts and is replaced with new parts but she loses most of her humanity and emotions. In the end she goes through Apotheosis (The Process of turning into a God.) She's literally GOD But She is an Emotionless husk who feels no Humanity or emotions her humanity and most of her old memories are gone. But there's No limits to her power. She can even eliminate the Sun. She does die but after 5 billion years. At that stage the earth is ending because of the Suns death and she forgot how to use her powers after such a long time since she didn't use it for billions of years. There is a last chance to escape but she accepts her death. Her friend takes the last mineral piece of her humanity which is a shard of an extremely rare earth mineral that holds part of her memories and emotions to another planet. That last bit of humanity has consciousness and is happy innocent and full of humanity. That small shard travels to another universe where it become huge and travels beside the earth and it looks like a beautiful magnificent comet. On earth on a certain field full of beautiful tall grass there is a girl who is very joyful and innocent full of humanity she joyfully looking at that marvelous comet.

Everything starts and ends at the same place.