Flandre Scarlet is the little sister of a vampire and a magical girl. She used to be secluded in the basement of the Scarlet Devil Tower. She is trying her best to cope with her desire to play with Remilia, who has disappeared because she has a certain duty to uphold.

Hong Meiling guards the gate to the Scarlet Devil Tower from the inside. She stands guard to protect her friends from the Witch of Scarlet Dreams. The Meiling of this Gensokyo doesn't sleep on the job because a single moment of carelessness could put her friends in danger. That's just how powerful the Witch of Scarlet Dreams is.

The tall scarlet tower grew so high that it touched the moon. This is because Remila was the first to confront the Witch of Scarlet Dreams and recognized the danger that she posed. Remilia ordered Patchouli to build the Scarlet Devil Tower to protect the residents of the Scarlet Devil Mansion.

The thoughts and feelings of the Witch of Scarlet Dreams, all alone on the moon, flowed into Flandre. These feelings became Flandre's memories in the form of a picture book. You and Reimu climbed to the top of the tower to resolve the Lost Word incident...

The Witch of Scarlet Dreams at the top of the Scarlet Devil Tower was waiting for a certain someone―a friend but also a rival. "I want to see her again! I want a battle of bullets with her again!" These feelings flowed into Flandre. She headed to the moon together with you and Reimu―to meet the Witch of Scarlet Dreams!