This is not a series per se but rather three connected one-shots.
It is correctly marked as "complete", since there is no way of knowing whether Sasada-sensei will write any further sequels.
The publication history is as follows: the initial one-shot was published in Hirari 9. Sasada then wrote a sequel to it for her tankoubon collection, "Kira Kira no Natsu" (whose cover appears on the series page.) A second sequel was then published in Hirari 10.