Hi Itou To me, the sentence says that it is the opposite to AJ's description. The tarrif is on American goods being imported to Japan. This makes it more difficult for America to sell into Japan, and that would be a reason for USA to feel that it is unfair and consider imposing sanctions. (These sanctions might be reciprocal import tarrifs imposed on Japanese goods, or even banning importation of some Japanese goods.)

I think you are asking: "What is the situation described in the below sentence?" >>> Unless Japan eliminates its unfair tariff, the US will impose sanctions. This means: Japan currently puts a Tarrif Tax on all products it exports. So things like PC's, Movies, Games, all have a tax added to their price if they are exported to the U.S. Since this sentence starts with "Unless..." it has a warning in it. So... if Japan doesnt remove their tarrif tax.... then.... what will happen? The US will impose sanctions (on japan). Sanction means to punish. So The U.s. will punish Japan (in some other policy or something that is not mentioned in this sentence). Example: Sony Playstation 5 is sold only in Japan. American children want to buy it, so they import it from japan. However japan has a tarriff, so the cost becomes $500 + $100(tax/tarrif). This makes people mad, so they complain. The governement thus decides to try and convince (or punish) japan that they will impose a sanction on japan, since Japan imports a lot of Beef and Milk from the US. Japan later decides to remove the tarrif because the cost of beef and milk has become too high. I hope these examples helped. Good luck.