Well, from the clip, the silhouette appears to wear a really long poofy skirt that covers her entire leg, so that can't be Reisen...unless she has alternate costumes, of course.
And oh yeah, the shadow figure seems to be holding something long like a pole weapon or something like that. It was very brief so I can't be sure.
So, I guess it is another character speculation time! Who could it be!?
- Kaguya, possible, the shadow figure fits her very well with her extremely poofy skirt, I don't recall her having a pole weapon though.
- Shou, I guess? She has a spear but her skirt isn't that poofy though, judging from her UFO art.
- Kagerou, again, the skirt looks a little bit too inflated to be her and I don't think she even has a weapon.
- Yukari? Keine?
- A new character?
- A Red Herring?
- Did you think the silhouette was someone else? Too bad! It was Kokoro-chan!
EDIT: The picture was really blurry so I couldn't see Reisen's hair. Yeah, it might be just her.