2009: Lost Memories
2002 South Korean action-adventure alternate history thriller. In 1909, Ito Hirobumi, then the Japanese Resident-General of Korea, survives his assassination from Korean nationalist An Jung-geun. Over the course of the 20th Century, the Japanese Empire remains a strong rising military power, and tightens its grip over Asia (particularly, for the story's purposes, Korea). Japan also allies with the United States during World War II, which ends with atomic bombs dropped on Berlin.
In ATL 2009, the Korean peninsula, as well as its people and culture, has been thoroughly Japanized. The protagonist is a Japanese government agent of Korean ancestry, who is put on the case of stopping an underground Korean nationalist resistance organization, bringing about torn loyalties.
Check out the intro timeline scene:
https://www.youtube.com/watch?v=--GdDrkp6IE