Remix is that thing where you get assigned an author and get to pick one of their fics to rewrite in your own way. It's a lot of fun; last year I got assigned peroxidepest17 and wrote Sixth Time's the Charm, if you want to see what they turn out like when I do them. Or hell, here's my whole remix tag which is all the stories I've either written for Remix, or have had remixed.
Right now there are only 2 JE authors signed up, including me. Um, that sucks. If you write NEWS/KAT-TUN/Arashi/Kanjani8, go sign up! I tried to work in juniors for you guys, but since the Ao3 mods can't tell us for sure yet whether we'd be able to tweak matches, I didn't want to make any promises I had to break afterwards. Hopefully next year all the shady business will be worked out.
Rules and FAQ here.
Signup link and directions here. This year they're running the exchange on Archive of Our Own because it automates a ton of the gruntwork, so if you need an invite code, go here and the mods will send you one quick.
Ask me other questions and I'll try to answer them? Obviously you can sign up for other stuff besides JE, but since that's all I'm writing this year, that's what I'm pimping out.