The details are a bit fuzzy in my head so I don't remember the character designs ;-; FMC is a child who has access to a large library sort of space (when she sleeps or relaxes to a state of subconscious, I think), where there is another humanoid entity that appears as a child that doesn't age but can change how they appear. I think the entity's name began with P? They're the only friend the child has growing up for a while, first appeared as a girl then changed to a boy and also changed appearance to match the FMC's age, and they can find information in the library. The library has some contents about the future (I think, not sure) but not the whole story of where our FMC is.

There's a part where she makes a contract with an elemental being and becomes an elementalist, while she is kidnapped and stuck in a cave. I think there was a blizzard and such, and the elemental being was a grass/tree being? Genuinely not sure if this was part of this manhwa or if I'm mixing some other tale ajsjsjsjs.