The Last Emperor by Aisin-Gioro Puyi (autobiography, 1964) — Puyi's account of his own extraordinary life, from the Forbidden City through Manchukuo to his re-education as an ordinary citizen under Communist rule. The Changchun chapters cover his years at the Imperial Palace of Manchukuo in vivid, sometimes self-justifying detail. The book was published in revised form under the title "From Emperor to Citizen" and is the primary source for understanding the Manchukuo period from the inside.
Manchukuo: The Creation of a State by Bill Sewell — a scholarly but readable account of how the Japanese puppet state was built, operated, and eventually collapsed. Essential context for understanding what you see when walking the Manchukuo sites in Changchun.
Under a Cruel Star by Heda Margolius Kovaly — not about Changchun specifically, but a memoir of life under totalitarianism that illuminates the same mechanisms of collaboration and resistance that characterised Manchukuo. Reading it alongside accounts of the Puyi years gives a clearer sense of how people navigate power they cannot refuse.
Pu Yi's Later Years by Li Wenda — covers the period from Puyi's Soviet capture through his time in a Chinese re-education facility and his final years as a worker in Beijing. Less well known than the autobiography but provides the outside perspective on a story Puyi told only from inside.