Pre-Lunatics depicts the events occurring shortly before and at the very beginning of case#0:lunatics. It shows a glimpse into Ryo Kazan's mental breakdown following the events of Moonlight Syndrome, Sumio Kodai leaving HQ after getting a bad feeling, and Tetsugoro Kusabi looking at a picture of Toriko Kusabi and Christina. It leads directly into lunatics, with its last few pages matching the beginning of the case.

(Source: Suda51 Wiki)