Allison & Lillia’s story covers the story from the Allison light novels for the first half of the series, and switches to the story from the Lillia and Treize light novels for the second half. Allison & Lillia is set in a world with onecontinent split down the middle from north-south by the towering Central Mountains, and the vast Lutoni River. Due to the geography, two cultures developed on either side of the divide. The eastern region is formally known as the Roxcheanuk Confederation, though more commonly known as Roxche (ロクシェ Rokushe?). The entire region comprises sixteen countries which all speak a common language. The western region is formally known as the United Kingdom of Bezel Iltoa, though better known as Sou Beil (スー･ベー･イル Sū Bē Iru?). This region comprises the two kingdoms of Bezel and Iltoa which both serve to bring together a small number of countries under the same common language as with that of the eastern region. There are more blond people in the west than in the east. At the time the story begins, it is year 3287 on the fictional universe’s World Calendar during summer. By this time, the two regions have been at war on and off for most of history, with the most recent hostilities breaking out some thirty-five years prior to the start of the series. An armistice has been in effect for the past thirty years, with only one major conflict during this time, creating a buffer zone thirty kilometers on either side of the river. The industry and technology of the world are roughly equivalent to the 1930s.
The first half of the story centers around Allison Whittington, a young blonde pilot in the Roxche Air Force who has experience with biplanes. She comes to visit her good friend Wil Schultz (short for Wilhelm, so pronounced Vill) during his summer vacation at Rowe Sneyum Senior School’s dormitory after being away for six months. Wil, who resides in Roxche, enjoys reading books, has a photographic memory, and is a good marksman. The two get involved in three different adventures over a period of a year where they meet new people and form important bonds.
The second half of the story starts about fifteen years after the conclusion of the first half. The story centers around Lilliane Schultz, or Lillia for short, the daughter of Allison and Wil. Wil has in this time assumed a new identity, Travas, under the Sou Beil military, though still dates Allison. Lillia’s companion is her childhood friend Treize, son of Carr Benedict and Fiona; Treize has a twin sister named Merielle. Lillia’s and Treize’s adventure together begins during her summer vacation from school.