I'm pretty sure that they are going to include their own storyline. I'm also a bit curious about how they are going to do the fights. The character's design looks a bit "soft" for anything too major to happen, especially for characters like Youmu and Sakuya who use weapons. Then again, I've seen a couple of videos where the characters look pretty cute, but they still fight all out.
Haha, thanks. She caught my heart ever since I saw her spinning in MoF.