From the artist's comment:

dA: KONNICHIWA FOREIGN EXCHANGE STUDENT FROM NIPPON. WATASHI WA DEVIANTART DESU. BUT YOU CAN CALL ME ONEE-CHAN. YOU’RE SO SUGOI IT’S PRACTICALLY KAWAII!!!!!! =^w^=
Pixiv: きもちわるい。止めて下さい。。。
dA: Eeeehhh? Nani~?

Pixiv-tan’s an overall nice, quiet, and polite girl. Pretty helpful when approached and easy to get along with. She’s really good at drawing so dA latches onto her almost like an annoying sidekick. Just like how dA takes some of Flickr’s photos, sometimes she takes Pixiv’s drawings and traces them. Pixiv kinda finds her annoying but since she’s nice, she just puts up with it. However, when she’s around her other Japanese friends (Nico and 2ch), she tends to talk smack about people here and there in Japanese. She’s got a few hikkikomori tendencies too. She also has an akita named Chobi. Pixiv’s got a couple of interesting quirks and she has a strange liking for alpacas.

And then there's Danbooru, Pixiv's North American cousin.

civilianscoot said:
And then there's Danbooru, Pixiv's North American cousin.

Cousin? More like stalker. Possibly yandere.