Plot
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 one continent 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 (ﾆ陳哉誰ﾆ歎ﾆ巽, Rokushe?). The entire region comprises of 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 (ﾆ湛ﾂーﾂ･ﾆ遅ﾂーﾂ･ﾆ辰ﾆ停?ｹ, Sū Bē Iru?). This region is comprised of 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 very few blond-haired people in Sou Beil. 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 ragging a war for the past 130 years, though an armistice has been in effect for the past ten years. 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. While out for a drive on Wil's motorcycle and run across an old man waiting on a bridge who is well-known in the area for telling false stories. They give him a ride to his home, and while there he tells them a story he claims to be true: that there is a treasure in the western region Sou Beil which could end the conflict between the warring regions. Before he can tell them more, a man who claims to be from the town hall takes the old man away, though Wil quickly notices that the man was most likely lying. Allison and Wil chase after them and find that the old man was taken away in a large plane. Allison and Wil steal a plane and chase the abductors across the river into Sou Beil; fortunately, they speak both languages. The first half of Allison & Lillia chronicle's Allison's and Wil's adventure as they go to rescue the old man.