New Light Novel announced:
http://www.mediafactory.co.jp/bunkoj/book_detail/909
This is a new Connect Light Novel - the first one was about Yozora and her point of view and that was also included in the first Anime season (Episode 12).
On the picture you can see a very young Sena (6-7 years old?) and the older girl on the right is Stella, it seems.