This anime is the perfect anime for those that watch a short serious invoilving mafia/gangster tropes.
The story revolves around a teen orphan boy who has struggled to survive a tough upbringing as he lost his parents at a young age. This boy has no reason to live other than to get revenge upon those who murdered his parents. To acomplish his one and only goal he must first get himself involved in the underworld he despises.
TLDR:
short, amazing charachter development and despite the bleak theme and atmosphere is extremely enjoyable to watch, mainly because of the great characters and their various compelling personalities.