I wrote earlier about the origin of the Japanese the ritual of chopping off pinkies. In Japan, the ritual comes the importance of the left pinkie in the grip of a Japanese sword. Removing the left pinkie is literally disarming and was used to punish people in the past. This has been ritualized and continues to be used by small number of Yakuza and others in Japan as a form of punishment or taking responsibility.
This is why I didn't understand why the Koreans were severing their fingers in protests against the Japanese. Two Koreans chopped their little fingers off in in front of the Japanese embassy in March to protest Japanese comments about the Dokdo islands and in 2001, 20 Koreans chopped their off their little fingers in protest against Koizumi's visit to the Yasukuni Shrine.
I was beginning to understand the issues that the Koreans were protesting against, but I didn't see how this finger chopping was involved. I decided to get to the bottom of this and asked friends during my trip to Korea.
Although it is an ancient custom, if I understand correctly, one of the most famous incidents was An Jung-geun, a legendary leader in the armed resistance against the Japanese occupation, chopping off parts of several of his fingers and writing "Korean Independence" in blood on the Korean national flag. Later he assassinated Japanese politician Hirobumi Ito in 1910. Hirobumi Ito was a key figure in the Meiji Restoration of Japan, former prime minister and former Resident-General of Korea. Using the blood from severed fingers to write such statements became a sign of solidarity in the resistance against the Japanese and I believe the recent finger chopping is a continuation of this.
I am not trying to make a statement about or a judgement on the anti-Japanese protests or the actions by the Japanese, but trying to clarify something that was confusing for me.
UPDATE: Edited post to reflect comments that An Jung-geun chopped his fingers before the assassination and that it's an ancient custom which didn't start with An Jung-geun.