In the latest issue of Famitsu, Square Enix has revealed that it plans to release special story episodes featuring Lightning.
Lightning will appear as a coliseum character and if you manage to defeat her, she will become a part of your party. Apart from Lightning, other classic Final Fantasy bosses will appear in the coliseum battle mode as well.
Square Enix even wants to expand on the Final Fantasy XIII-2 story beyond just DLC. Depending on the demand, they could release novels and other things to expand on the Final Fantasy XIII-2 universe.
Final Fantasy XIII-2 is out January 31st in North America and February 3rd in Europe for the PS3 and Xbox 360.