“I feel like my headaches aren’t so bad at dusk. I think tonight’s the night― Ouch. Maybe not…”
Rumia is an unnoteworthy youkai who eats humans, despite only being marginally stronger than them. Her ability to manipulate darkness sounds powerful, but she remains an ordinary youkai, never getting involved with Gensokyo’s incidents. In fact, that’s the case for Rumia in every world… or is it?
During a certain incident, the scarlet mist wasn’t the only thing protecting the vampires from pesky sunlight. What follows is a clearly false information regarding said incident…

Only a few people were able to realize the incident had been prolonged.
Firstly, those capable of seeing the future could clearly tell something was wrong when events unfolded in a different way than they expected.
Then, there were those with the power to determine the future themselves. Having an array of schemes (some well-intentioned, some evil) in motion and control over those less powerful than themselves, they were able to conclude something was wrong when unforeseen events occured.
Finally, there were those who had already experienced the future. Their existence was predicated on the cyclical nature of time.

The Prolonged Scarlet Mist Incident
The Scarlet Mist Incident began with a vampire’s simple desire to block out the sun and walk around outside during the day. Based on the currently available historical records, it seems this incident saw the first use of a Spell Card. The incident was resolved by a shrine maiden and a magician, who stormed into the Scarlet Devil Mansion and defeated the head vampire, thus stopping the scarlet mist from fully covering Gensokyo. After that, the shrine maiden and the magician became friends with the vampire, her little sister, and all those who lived in the mansion. It was almost as if the entire incident was an elaborate scheme to train a new generation of bullet battlers.
Rumia had nothing to do with the incident. That said, she loved being surrounded by the scarlet mist and had a super fun time. In that way, she was an unexpected beneficiary of the incident―a freeloader, if you will. (Normally, the countless fairies in Gensokyo make up the bulk of incident freeloaders.)
With her ability to manipulate darkness, Rumia would’ve made a useful ally for the vampire, but as stated earlier, she never got involved. At least, she didn’t in worlds where history followed its proper course…

Universes containing an EX Factor produce EX Beings, who, in turn, cause prolonged incidents. Who can and can’t become an EX Being is currently being investigated, but the following information has already been confirmed. Firstly, the same prolonged incident can have multiple EX Being suspects. Secondly, multiple EX Beings can exist in the same world.

As a historical fact, Rumia had nothing to do with the incident. If in some world, she did, that may be due to one of the following reasons:

1. There are historical documents pertaining to the incident that are yet to be discovered.
2. It is a world built on a false premise, perhaps one stemming from a forged historical document…
In this case, the latter is true. There are currently no trustworthy historical documents detailing the connection between the Scarlet Mist Incident and the Vampire Incident. Whether they are connected at all is still unknown. However, a decidedly untrustworthy document makes mention of “the great Scarlet Devil’s favorite parasol,” “the Scarlet Devil’s maroon knight,” and “the devil-possessed youkai.” Combining that with the ofuda ribbon Rumia wears… What does it all mean?