WMG / 2009: Lost Memories

Sakamoto never restored the timeline. He merely created a new timeline merely by his appearance.
The fact that the new timeline had the North and South Korea reunite in 2008 may imply that Sakamoto even tampered on the communist faction, eliminating those who he think will do more harm than good in a liberated Korea.
China and Japan substituted places in World War II.
It would make sense since the Chinese at that time were supplied by Nazi Germany. That's why Japan was allowed to take Manchuria from China.
Sakamoto's mother secretly taught his son Korean.
That would explain how he is able to speak Korean fluently.
The alternate timeline's 2002 FIFA World Cup.
Brazil still won but, unlike the original timeline, where the Brazilians won all matches they played, they lost their first one during the round robin stage.note 

Brazil and Turkey still played against each other during the semi finals but the other semifinalists were Spain and Japan instead of South Korea and Germany.note 

Germany's best players in the original timeline were either killed or never born in the new timeline because of the atomic bombs.

Japan lost the semi finals. Otherwise the result would be announced along with the fact Japan was the cup's only host in the alternate timeline.

The Korean stadiums that were used for the cup in the original timeline were used in the alternate one as well. Japan is credited as the only host because Korea is part of Japan.
Captain Tsubasa Road to 2002 takes place in the alternate timeline.
That's why that story doesn't mention any Korea as co-host.
The Chinese boycotted the Olympic games held in Japan.
Not only those that were held in Korea in the original timeline but also the Tokyo games back in 1964. It's retaliation against the Japanese for taking over Manchuria.
The Korean researcher planned to use the artifacts to make Korea overthrow Japan.
Unfortunately, for her, Inoue had plans of his own and she realized the best she could do for Korea was to foil them.
Inoue exists in the new new timeline created at the end of the movie.
He'll seek the artifacts like in the original timeline only to find out they're too damaged to be used. The frustration will drive him to suicide.
http://tvtropes.org/pmwiki/pmwiki.php/WMG/TwoThousandAndNineLostMemories