Mumei is apparently the body Set was inhabiting back in the main game, and wanted the protagonists to finish them off-thus getting the main cast to cause a ruckus again.
That's probably why it's got some of Set's theme in it. The other reason being the survival spell.
It's a very jazzy theme, which I wasn't really expecting, but it's nice nonetheless.
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The soundtrack comes from 東方真珠島 ~ Hollow Song of Birds, a Touhou fangame by Kaisendo (海鮮堂).
You can download the game here:
www.freem.ne.jp/win/game/19424
You can also directly support Wanwan and get the soundtrack here:
wanwan.bandcamp.com/album/hol...
Song: Glass Heart Chevalier (グラスハートシュバリエ)
Composer: Wanwan
Portrait: ANMITA
6 июл 2019