All the basic information here was taken from Wikipedia so if you want to know more about them you can go there :).
First let's start with Iori, our red-haired seme boy... Well, Iori Yagami is a character from the SNK Playmore's The King of Fighters video game series that first appeared in The King of Fighters '95 as the leader of the Rivals Team. He is an iconic character of the series, and regularly appears on publicity material and merchandise. Iori is a central character to the series' plot, and the initial enemy and eventual rival of Kyo Kusanagi. He was created specifically to become Kyo's rival as his name and abilities were designed to relate him with the Yamata no Orochi legend. The designers ended up liking him so much that they take care how his character is developed along the series.
Iori is the heir of the Yagami clan, who wield pyrokinetic powers and sealed the Orochi demon along with the Kusanagi and Yata clans. However, after betraying the Kusanagi clan, the Yagami are cursed by Orochi giving them powers that cause all members to die young. The character harbors hatred against the other clans, but later becomes obsessed to kill their heir Kyo. Due to that, Iori sometimes helps him in order to have the opportunity to have a final fight against him. Aside from the main series, Iori appears in several other media series such as spin-offs and crossover video games, and comic adaptations of the series.
And so Kyo Kusanagi appears! The ukerival of Iori.. Kyo Kusanagi is one of the main characters in SNK Playmore's The King of Fighters video game series; he was first introduced in The King of Fighters '94 as the leader of the Japan team. He is one of the iconic characters of the series and regularly appears on publicity material and merchandise. His name and abilities were designed in order to relate him with the Yamata no Orochi legend. Due to the fact he was highly popular and his outfit changed along the series, the designers created a few clones with his old appearance.
He enters every The King of Fighters tournament representing Japan and uses his clan's fighting style to combine fire with kenpo. Aside from the main series, Kyo also appears in several other media series such as spin-offs and crossover video games as well as comic adaptations of the series.
And that's all about them, or at least the most important information you need to know. Now, with the fangirlism.. Okay people, you can't deny that there's an attraction between them, beyond the rivalry that has existed between their clans, this is the present, and they are they, so the important thing is what they feel, wich is love, you know, between Love & Hate.. There's one step, aaaand they passed that step, besides, Iori & Kyo are obsessed with Each Other ... They must fight, they must feel, they must be the same. And the phrases that Iori always tells to kyo reveal much more than a desire to fight, Iori wants to be with Kyo but his cold-hearted side sometimes makes that impossible, but Kyo always understands what he just said or felt. They are meant to be together. So yay for the fandom! :D

A Fanlisting? If you're still wondering what is a fanlisting, the fanlistings.org points out that: "A fanlisting is a place for all fans of a particular show, movie, actor, actress, singer, etc. to come together and build the biggest listing of people from all around the world who are fans of that subject". So... in other words, is a listing of fans about a main subject where you join with your name, e-mail adress and your country and show your... fan love? XDDD.