The "Big Girl" is seen in various scenes throughout the game looking through a book. Her name is unknown, but she appears to be gather information or evidence that the tiny people actually existed. Her life is implied to have taken place much after the events of TinyWars. She does not directly interact with any of the characters but is seen as a historian or an evidence collector for the history of the tiny people.
The book is used as a theme for the menu. Whenever new characters are unlocked, their corresponding items or weapons appear as items taped to the first page of the book within the menu screens. It is presumed that the title of the book is called "TinyWars" and contains various notes and evidences for the tiny people's existence.
She appears in various scenes through John's House. The window behind her in some scenes matches the window seen on the outside of John's House, which appears to be the attic or a top floor bedroom.