The artist used this random online generator.

Shindanmaker: 東方簡単お題ッター
("Suggesting to you a Touhou-themed subject which you are supposed to draw today. The result changes every day.")
http://shindanmaker.com/5317

"Today, Gaoo's subject is 'Okuu who has lost something precious.' Good Luck!"

So did she lose her control rod, her third eye, or her virginity?

Looks more like "that hole in her heart" to me.
But the dark, soulless eyes might tell a different story...

DeinGott said:
Looks more like "that hole in her heart" to me.
But the dark, soulless eyes might tell a different story...

Eh? She looks pretty happy to me.

Part of the commentary:

お空ちゃんは何を無くしたのかな？。

「お兄さんがお兄さんと思える感覚かな。これからもよろしくね。お兄さん。大好きだよ。お兄さん・・・。」

henmere said:
Part of the commentary:

Anybody kind to transalte?

I can't give this a good translation, but the translation machine says something to the effect of:

"What did Okuu lose?

The sense that her onii-san was still her onii-san. (Link goes to incest tag.) Please take care of me from now on, Onii-san. I love you, Onii-san."

NWSiaCB said:
I can't give this a good translation, but the translation machine says something to the effect of:

"What did Okuu lose?

The sense that her onii-san was still her onii-san. (Link goes to incest tag.) Please take care of me from now on, Onii-san. I love you, Onii-san."

Thank you

Huh, the machine translation was spot-on for a change.