Buffy and Spike are Champions

I am looking for a fic where Buffy and Spike are brought to another dimension because the people there called for a champion and they were both pulled into the portal. The people see them both as Champions as they both came through the portal. I remember they had to fight something that I think was destroying entire cities. I cannot remember the name of the author or title of the fic.

That's it! Thank you so much.