Back in the 1980s and 1990s, there were numerous anime OVAs (original video animation) that told grisly, gritty, and grimy stories. Full of blood, guts, gore, and all manner of other "adult" content, these projects were instrumental in positioning anime as the "grown-up" cartoon alternative in the West. Some of these OVA movies and TV shows were based on manga, though in some cases, this source material was never actually completed.
Source：https://www.cbr.com/genocyber-manga-never-finished-why/
