Time to talk about the silhouette. We've got some good guesses in this thread!
The following ideas are a result of my discussion with friends, although people here and on Japanese forums have come to similar conclusions.
Almost unquestionable:
The shapes to the upper left of the logo are her fingers. She is holding one hand up, with her palm pointing to the sky.
Unconfirmed but likely:
1. The floating objects resemble masks: flat objects convexing on one side.
2. Reading of her pose depends on which hand she is holding up. If it's the right hand, then her pose probably resembles Ran's SC pose, with right arm up, left arm at her chest.
More likely, it's the left hand. She is stretching her right arm out while holding something in her hand, and putting her left hand up near her face. Her legs are also crossed. She is dancing
3. What has both masks and dancing? A masquerade.
Speculation:
There are two related important activities in Japan that involves masks and dancing: kagura, the Shinto ritual dance, and noh theatre.
A ritual dance has been shown in Touhou before, when Yorihime summoned Amaterasu. The HM character's dance might be even closer to a real shrine maiden's, since she's holding some artifact in her right hand. Alternatively, it could be another mask in her hand. Yes, she is very likely a Shinto shaman/priestess, just like Reimu, Sanae, Yorihime and Futo.
The most famous kagura dance in mythology is that of Ame-no-uzume, which is one of the three things that caused Amaterasu to come out of hiding from a cave. Later Ame-no-uzume would serve under what would become the imperial family, and in one legend, marry Saruta-hiko and begot the tengu race.
we've also brought up Ame-no-sagume. She's a servant of Ame-no-wakahiko, the first messenger Amaterasu sent to Izumo. She has also been speculated by scholars to be a symbolization of shaman. In folklore, she may have become the demon Amanojaku, which we've already discussed here.
Considering the sacred kashiwa leaf in the logo, associated with the high priests, the HM character may indeed be a messenger from high above, just like Ame-no-uzume or Ame-no-sagume. She's also likely to have a strong noh motif.