You don't need to know the Story of Girls' Frontline. Information about Stuff out of Girls' Frontline is in the Glossary.

"A lost Doll" plays in a post-apocalyptic world set in the Girls' Frontline Universe.
Follow a broken G41 through a War ravaged world after the War ended and uncover what mystery lies in the Past.

The Story is going to focus mainly on the Past of G41. Her experiences in the new world and the exploring of it.

A quick disclaimer
While I know some of the Girls' Frontline Story and have read Story and Lore, there will be mistakes and things that don't fit the Game Lore.
The Story doesn't play in the Timeline of the Game.

Yes I know, that I am bad at Writing a Description.