This is one of those hidden gems in anime that you are glad to find. I believe that this anime doesn't get the recognition it deserves, because this is surely a deeply emotional, engaging story with heart and substance.
There are a lot of lessons to be found in this anime, from friendship to perseverance, hope but also about the cruelty that humans are capable of. Also, this could be seen as a sociological critique of post-ww2 Japan, showing some of the ugly truths we don't want to know about.
This anime focuses on young men abandoned by society, and while they are imprisoned, they are far for being bad people. The viewer can realize that true friendship and bonds can be found even in the worst places of earth, and that nobody should give up to hope and dreams, regardless of their background.
Not perfect though, i believe that the anime sometimes is a bit indulgent in giving the viewer a "happy" resolution to almost all of the mini-stories going on with the characters, and i feel that the anime didn't reached it's full potential in depicting the cruel side of prisons, and human beings. It is like... it can get pretty dark, but i feel that the author was concerned that the viewer wouldn't be satisfied if the anime were too pessimistic.
In the end, this is an excelent anime, one of the best seinen out there, and ayone looking for a mature story, albeit dark at times but with a glimp of sunshine, you can't go wrong with this.
