The official website of Seikon no Qwaser
accidentally leaked a new anime "Seikon no Qwaser: Empress no Shozo". It was supposed to be posted on June 20th and the announcement has already been erased. Judging from the subtitle, the new anime will be based on Ekaterina Kurae
's episode, the chapter 16 of the original manga.
Source: Screenshot of the announcement
Updated on June 20th
The announcement was re-posted in the official website.
Qwaser official website
Updated on July 15th
According to Akita Shoten's notice to bookstores, the new anime is an OVA to be bundled with the original manga volume 10. It will be released on October 20th.
Source: Scan of the notice