The concept is developed by someone known as Kaori Mystique, or Melody Harmonia.
The girls have been given an invitation to a party by a mysterious two-headed creature. A cat head was on one end while a dog head was on the other. The heroines notice the weird-looking creature and take the invitation. The invitation read:
"Party at the Jumpscare Manor
Wear your best attire and be sure to bring a guest along. We'll be eagerly waiting for your arrival♥
From, S. Hashimoto"
Yukari Yakumo reads the invitation and is ecstatic when she reads that the party is being held at the mansion of an old friend of hers, so she drags Reimu Hakurei and her shikigami Ran Yakumo along with her.
Shortly after receiving her invitation, Marisa Kirisame discovers a divine spirit known as Rin Satsuki playing her erhu in the Human Village, but not many people were willing to listen to her music. Needing a partner to attend, she convinces the spirit to join her by agreeing to help her attract more people to listen to her music if she agreed to be her partner. Rin agreed, and the two set off for the mansion.
Remilia Scarlet accepts the invitation because she was bored and she likes parties. Sakuya Izayoi simply goes along in order to keep the mistress out of trouble.
Meanwhile, while Youmu Konpaku was going out to Eientei in order to pick up some medicine for Yuyuko who had come down with a cold, she encounters the two-headed creature with the invitation. She reads it and suspects there was something about it. She then encounters Fujiwara no Mokou who then guides her out of the Bamboo Forest after picking up the medicine. Youmu tells Mokou about what she discovered and Mokou agrees to go along with her since she had nothing else to do.
But the other girls will soon find out that what they hoped would be a party turns out to be something much bigger....
- Reimu Hakurei and Yukari Yakumo with Ran Yakumo (Grotesque Barrier Team)
- Marisa Kirisame and Rin Satsuki (Divine Magic Team)
- Remilia Scarlet and Sakuya Izayoi (Elegant Scarlet Devil Team)
- Youmu Konpaku and Fujiwara no Mokou (Immortal Netherworld Dweller Team)