When I heard of it for the first time, I couldn’t stop laughing though I had no idea what this term means…XD Well, キモイ[kimoi] is an abbreviation of 気持ち悪い[kimochiwarui], which means hideous, grotesque, annoying, unpleasant, uncomfortable, and so on. 同盟[doumei] means an union or an alliance…So literally, this means a brigade(I wanted to use brigade after SOS brigade ;^^) for enthusiastic fans of hideous characters.
At any rate, these brigades are made by enthusiastic fans(cult?) of a certain character(mostly male characters) from anime, manga or whatsover, for fans. The important thing is that those fans love such hideous characters for some reason. This “hideous” does not even necessarily mean he is not good-looking, but extremely geeky, narcissistic, or hentai(perverted). So speaking of those characters who are supported by キモイ同盟, I shall mention Light Yagami, L(Death Note, see above images), Yuushi Oshitari(Prince of Tennis, see below image), Takaya Abe(Ookiku furikabutte, see below image. But in his case, it is written as キモベ同盟[kimobe doumei]. I guess it puns upon his last name) and so on. No matter how narcissistic he is, no matter how hentai taste he has, she can’t help but loving him…Yes, in order to meet someone who has the same taste, and share it, they unite as a キモイ同盟. So they can pep themselves up each other…
If there’s no fan of your favorite character around you, and if he is not much popular because he is such a hentai, all you have to do is either open up or go to a キモイ同盟. You can find your alliances there. :)
By the way, I just took a quick look at the certain キモイ同盟 for Light Yagami a while ago. And the first passage starts with ニア(Near; L’s heir)死ね死ね死ね死ね死ね死ね…[Near, die die die die die die] it seems to last forever. ｶﾞｸｶﾞｸ(((；゜д゜)))ﾌﾞﾙﾌﾞﾙ It sounds like a real Kira-cult, doesn’t it?