So... is Rainbow: Nisha Rokubou no Shichinin finished or not?
NO, it is not finished.
Why?
The anime finished after the manga:
Anime finished: September 29, 2010
Manga finished: January 04, 2010
... But MangaUpdates contains information about the anime adaptation and indicates that it is incomplete.
Watching Order (by release date)
Here you have all the anime relations we detected ordered by release date, so you can see the reason for this status in context and also use it as watching order.
The mangas and the non-core contents are excluded by default, but you can enable them by clicking the buttons below:
Synopsis
Rainbow: Nisha Rokubou no Shichinin tells the story of seven young men incarcerated in a Japanese reform school in the 1950s.
Upon arrival, the six newest inmates, guilty of various crimes, are placed in the same cell where they meet Rokurouta Sakuragi, an older, more experienced prisoner and former boxer.
Rokurouta becomes a mentor figure, offering guidance and hope to the younger men and fostering a strong sense of camaraderie among them, encouraging them to look forward to their release.
The series focuses on their daily lives and the harsh realities of the reform school, including the brutal treatment they endure at the hands of corrupt staff, specifically a sadistic guard and a depraved doctor.
The central narrative revolves around their collective struggle for survival, their efforts to maintain hope amidst despair, and the question of what awaits them in the outside world after enduring such hardship and trauma.