Kyoko and Yuki are the main antagonists of the TV special "iGo to Japan" of iCarly. Two evil Japanese web comedians that tried to sabotage Carly, Sam, and Freddie's chance of winning the iWeb Award.
Both groups were in the running for the award and considered each other strong competition, even intimidating the iCarly crew, somewhat.
On the other hand, Kyoko and Yuki feared the influence of iCarly, and plotted to eliminate them from the equation so they could have a higher chance of winning. Initially, the duo acted as friends to the iCarly gang, but eventually show their true colors when they drive to the middle of nowhere, leaving the three stranded and lost, while they would try to win the iWeb Award by default, (due to iCarly being a no show).
However, due to Spencer, Mrs. Benson, and some quick thinking, they were able to make it to the event, and won the award. Afterwards, the siblings got arrested for kidnapping the iCarly team.
As seen during the fake fight they set up to trick the iCarly gang, they are both accomplished martial artists.