From the poofy shoulder and sleeve frill, I'd say that's Remilia's arm. Tag-worthy?

I was thinking the same thing.

Added since it's the focal point of the story.

Remi's arm is going to get broken...

From Pixiv:
remirya:花見で酔ったフランに抱きつかれたなう
sakuyan:お嬢様が幸せそうなう
rerereimu:我に返ったら噛まれるわね
remirya:@rerereimu　後のことは後のことだァー！！
momotenshi:紅魔館に血の雨が降る・・・
remirya:@momotenshi　五月蠅い黙れ
momotenshi:@remirya　『』

In short, Flan is drunk from the flower viewing, that's why she's hugging Remi's arm. While Sakuya is saying that Remi was fortunate, Reimu said that Flan will bite Remi when they get back. Remi doesn't really care. Tenshi said that Scarlet Devil Mansion will be raining blood, resulting Remi to tell her to shut up.

If I messed up any part, please correct me and sorry...

And so, Flan makes the 100th page of Disgustingly Adorable. Congratulations to her and to everyone at Danbooru.

remirya: Flan got drunk while flower viewing and is hugging me NOW
sakuyan: The mistress looks quite happy NOW
rerereimu: When she comes to her senses, you're going to get bitten
remirya: @rerereimu What happens later is for later!
momotenshi: It's raining blood at the SDM...
remirya: @momotenshi Shut your mouth.
momotenshi: @remirya ""

May as well just translate it if you're going to go to the trouble of understanding it, I say. Also, 幸い has to do with luck, but 幸せ is more just plain happiness.

Whew,finished reordering the pool.However,post#856601,#856602 and the last four of the pool are not in the files I have,so I don't know what to do with it.