I wonder if this mightn't turn out to be a longish story.
pixiv's userbase said: Wh-who are you!!? It can't be, the Masked Hakurei...!! Masked Hakurei... who could it be? Touhou Tag Dr... wait what? deus ex machina Do you know, Raiden?! The comments field was trained a mysterious person of mystery
The "Do you know, Raiden?!" line appears to be some sort of a meme related to sudden revelations about an enemy, but I couldn't pin down an exact source or meaning.
知っているのか、雷電! ("You know this one, Raiden?!") comes from Sakigake! Otokojuku, a martial arts comedy manga; Raiden, due to his extensive martial arts training, was generally able to recognize and explain opponents' fighting styles and special techniques and often delivered exposition about them, triggering this line from his companions.
Is this really "Masked Hakurei" or "Masque d'Hakurei" (or "du Hakurei", maybe)? I only ask because I'd expect "masked" to be マスクド, but Ao Usagi's parsing it as マスク・ド...
...as much as I hate to say it, we'd be no match for her.Calm down, Cirno!If that woman really did kill Reimu...To be continuedDamn it! I'll avenge you, Reimu!You don't think Reimu was killed by that guy, do you...?