2009 Lost Memories

Joint Japanese-South Korean sci-fi action thriller from 2002.

It's 2009 in an Alternate History where the assassination of Resident-General Ito Hirobumi in 1909 was averted, leading to Japan allied to the US in World War II and therefore retaining its colonial empire including Korea.

Sakamoto, a Japanese Bureau of Investigation (JBI) agent of Korean heritage and Saigo, his Japanese partner try to solve a strange case where Pro-Korean nationalist "terrorists" attempt to steal a strange archaeological artifact. Initially Sakamoto is valuable to the case because of his ability to communicate with the terrorists. He is later removed from the case when it is discovered that his father had some previous involvement with the terrorist group. Sakamoto's desire to solve the mystery involves threatening the powerful Inoue Foundation. This only makes him more passionate about its resolution and after uncovering more on his own, he discovers that reality isn't how it should be. It then becomes his new mission to restore history to its rightful path.

Essentially Fatherland with an Asian slant.

Contains examples for the following tropes:

 * Alternate History - Ito Hirobumi survives his assassination attempt at Harbin 1909.
 * Bittersweet Ending -
 * Butterfly of Doom - The conspirators of the Inoue Foundation explain Saigo thoroughly that he and his family won't exist in a world without a surviving Hirobumi, so that he cannot renounce to follow the call. Considering what the butterfly effect is all about, it's completely Justified.
 * Chekhov's Gun - The Lunar Crescent, the device enabling the devastating time traveling act in the first place. Also qualifies for Artifact of Doom.
 * Culture Police - Koreans with perfectly Japanese names like Sakamoto and Takahashi? Kyongsong/Keijo (Seoul) looking like a thoroughly Japanese city with abundant Hiragana instead of Hangeul? Koreatowns in a Korean city? Tokyo must have played an awful one.
 * Dressing as the Enemy - Not really as the enemy considering which side Saigo is on in 1909, but he still kills one of the guards to take his uniform and mesh unnoticed among the other guards at Harbin station as the only savvy Japanese to protect Hirobumi from An's shots.
 * Exty Years From Now - The whole story is to take place a whole century from the assassination (attempt) on Ito Hirobumi and provoked The Great Politics Mess-Up by setting the story Twenty Minutes Into the Future.
 * Fatal Family Photo - Inverted. Sakamoto finds a photo with the guy he shot down in the beginning and his little son whom he's hiding with in the resistance cell near the end of the movie, mere moments before said little son is gunned down (among others) himself by JBI forces.
 * For Want of a Nail - The survival of Ito Hirobumi ensuring the hegemional power of Imperial Japan.
 * Girl of My Dreams - Sakamoto instantly dreams of a girl wearing the story relevant crescent on a chain of hers. He gets to know her
 * Government Conspiracy - The JBI and Inoue Foundation are obviously in cahoots together.
 * He Knows Too Much - Sakamoto's father.
 * Heel Face Turn - Sakamoto
 * Heterosexual Life Partners - Saigo and Sakamoto, even at the final showdown
 * Historical In-Joke - After Sakamato answered his father's mentor's question if he knew who An Jung-geun was ("the assassin to kill Ito Hirobumi"), the aforementioned mentor replied that "assassin is an accurate word, because he did indeed succeed", before proceeding with Sakamoto's initiation into the manipulated nature of their timeline.
 * Imperial Japan
 * Istanbul Not Constantinople - Seoul is Kyongsong, Korea is Choson instead of Hanguk. In Japanese, this would be Keijo and Chosen, respectively.
 * Just a Stupid Accent - The fact that Sakamoto not only speaks Korean fluenty, but also speaks Japanese with a Korean accent, despite the claims that Sakamoto grew up in a totally Japanese environment.
 * La Résistance - The Hureisenjin, the Korean freedom fighters
 * Named After Somebody Famous - The employer of police officers Saigo and Sakamoto, the Japanese Bureau of Investigation (JBI). We may assume that the producers didn't care in the first place why a domestic intelligence service needed the word "Japanese" in its name.
 * Enh, it's not unheard of; e.g. United States Secret Service (USSS), Royal Canadian Mounted Police (RCMP), Australian Federal Police (AFP).
 * No Koreans in Japan - Or rather less and less Koreans in Japanese Korea. Also see Culture Police.
 * Punch Clock Villain - The movie is credited for being a Korean production that depicts Japanese people differentiately and not as complete monsters per se.
 * Reality Subtext - The whole movie is nothing else than a promotion for Korean reunification, saying that a unified Korea would even be more of a tiger than South Korea has already been. Suffice to say, a reunification of Korea would in reality be just multiple times as costly and difficult as that of Germany could have ever been.
 * Terminator Twosome - Saigo and Sakamoto struggling to avoid or ensure Ito Hirobumi's assassination.
 * The Great Politics Mess-Up - Invoked and failed. According to the movie, the two Koreas were supposed to unite in 2008, enabling Korea to become a new star on the international scene. Flash forward to 2010, the Kim dynasty is just preparing its reproduction into its third generation and the People's Republic of Tyranny is going on like it's always been.
 * Time Travel
 * Twenty Minutes Into the Future - Played deliberately.
 * Well-Intentioned Extremist - You may argue if the intentions justify the means even in the eyes of the fellow Korean that put up with being part of Japan (as they explicitally became more extreme as native support decreased), but you may grant the Hureisenjin captors for not abusing their hostages as human shields. They just want to catch the artifact.
 * Written by the Winners - In the timeline, the March 1st Movement of 1919 is referred to as a terrorist uprising.
 * You Killed My Father
 * Sakamoto learns during his Heel Face Turn that the truth about the "corruption" his father did as a police officer and put him on death row was that he worked with the Hureisenjin.
 * Sakamoto also gets to know the little son of the guy he shot down in the beginning. He also finds the Fatal Family Photo moments before said little son gets gunned down himself, despite Sakamoto trying to save him. This causes severe trauma.
 * Your Terrorists Are Our Freedom Fighters
 * Zeerust - The video phone booth, outdated even when the movie was made, especially in Korea and Japan. Even dealing in an alternate timeline won't make it forgivable.