What are Sliders? they are what is called Isekaijin in Japanese. On this site the are World Travelers, Otherworlders, people from another world. On episode 24 chronologically in the tv anime, while Kyon was recalling scenes that happened during the time people were preparing for the cultural festival. 3 images popped up of people who were dressed in clothes from a fantasy setting. 2 of which I will show here. Spoiler Spoiler While I initially did not notice anything out of place, when they were mentioned all of a sudden while I was rewatching the series I figured it out since Kyon mentioned that they were not part of any programs in the festival. I am also trying to edit the wikia page, but it is protected from editing. This info needs to be added under possible suspects.
did the yuusha also got summoned do your best please before you sacrifice yourself though. Donate all of your nuffies to us
They mentioned them too in the novels, but at the time I thought they were ESPers, time travelers or aliens working behind the scenes. I also harboured the suspicions of them being people from different dimensions brought Haruhi Ex Machina, but I believe I settled for the explanation I gave at first. Missed them in the anime, though.