artist:
マスク・ド・ハクレイ　第一話

.結構長い話になるかもしれません

Tags　だ、誰なんだー!! 　まさか、あのマスク・ド・ハクレイかッ! 　マスク・ド・ハクレイ…一体何者なんだ 　夢の東方タ・・・あれ? 　御都合主義 　*東方 　*漫画 　知っているのか、雷電! 　訓練されたコメント欄 　謎の怪人

I think that person is Reimu's brother.

Ao Usagi said:
The Masked Hakurei: Chapter 1

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.

MGS2, maybe?

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.

So does this count as touhou tag dream tribute?

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...

I was thinking 'du hakurei' as well...