Remilia Scarlet is Flandre's older sister and the vampire mistress of the Scarlet Devil Mansion. One night, she stood on the mansion's terrace and desperately tried to quiet the blood rushing through her veins while staring up at the scarlet Moon.

Flandre Scarlet is Remilia's younger sister and the vampire shut-in of the Scarlet Devil Mansion. On the same night, she also tried to quell her raging blood as she felt the influence of the scarlet Moon far above her.

Sakuya Izayoi takes care of, protects, and satisfies the whims of the Scarlet sisters as one of the Scarlet Devil Mansion's servants. She quickly devised a plan after observing the scarlet Moon's effects on the vampire sisters and evaluating that no good would come from leaving them to their own devices.

The Scarlet sisters were stressed out from trying to contain the violent urges instigated by the scarlet moonlight. If they went on a rampage, they would certainly tarnish their reputation with their fellow denizens of Gensokyo, particularly with a certain few. That's why Sakuya had to act. She quickly prepared a marvelous stage to host the Blood Moon Singing Contest.

The Blood Moon Singing Contest kicked off with a special duet by the hosts―the Scarlet Sisters. And, as it happens, this was also the final performance of the night. Typically, the judges would ring a bell to signal the end and usher in the next contestants, but that was never going to happen in this instance. Sakuya was the sole judge, and she was content to watch and listen to the sisters sing all night long. In the end, it seems her plan didn't exactly improve the Scarlet Devil Mansion's reputation either...