Who is this?

There's a touhou tag, so joutouguu_mayumi, maybe?

Kissmyaxe said:

There's a touhou tag, so joutouguu_mayumi, maybe?

That's a good guess based on the hair. I went ahead and dug out an old tweet, the artist used a vocaloid-themed randomizer which described a blue-eyed, blonde-haired girl with short twintails. I guess she's an OC?