The way this story will work is, each chapter, a new author will write it. The author writing the chapter, goes off the summery, but can change the story line as they go, not too much though.
If you would like, you can add your OC's into the story, but they CAN'T be a major part. The story has to stay mainly on DiegoxShira. And keep in mind that the authors after you, have to work with that OC as well.
If you want to write the first chapter, or have any questions, send me a PM.