Strike Witches: Kimi to Tsunagaru Sora

The Sky That Connects Us, often referred to as "Strike Witches 1.5", is a manga that was published in Nyantype magazine. Additionally, a Tankouban version with all eight chapters was published by Kadowaka at the end of September, 2010. It spans the time between the two seasons of the Anime. It covers the activities of the various members of the 501st after it was disbanded following the destruction of the Neuroi Hive above Gallia.

(Source: Strike Witches Wikia)