Ima, Soko ni Iru Boku, Rainbow: Nisha Rokubou no Shichinin Recommendations
Both shows are extremely depressing and dark. Both focus on prisoners who want their freedom restored.
Ima, Soko ni Iru Boku revolves more around war, its consequences, power, corruption etc.
Rokubou no Shichinin on the other hand focuses more on the personal lives of the main characters, their bond and how they face challenges together.
If you liked one, give the other a try.
the vibe is very similar.
the brutality of the world yet the hope within friends and the changing of the heart.
if you liked this anime definitely watch the other