Short stories taking place both before and during the main Ajin series.
The first is a prequel focused on drama featuring Shinya, a university student who discovers that he’s an Ajin following a fatal motorcycle accident. The second is a collection of comedic ‘behind-the-scenes’ character-based segments, each of which takes place at a different part of the parent series. The third is an action-centric prequel centering on the event that triggered Satou’s transformation from soldier to terrorist.
More Information:
aniDB
Wikipedia